An error occurred when syncing with a Microsoft 365 calendar. This used to work fine. Removing all app data and re-adding the account did not help.

Nullable object must have a value.

Action: ReceiveCalendar

Calendar: Calendar

System.InvalidOperationException: Nullable object must have a value.

  at System.Nullable`1[T].get_Value () [0x00008] in <c8188c599aa44ff5949719d679dd5268>:0 

  at XCalendarApp.MicrosoftGraphProvider.ProviderTypes.Event.GetTZOriginalStart (XCalendarApp.MicrosoftGraphProvider.ProviderTypes.Event seriesMaster) <0x752d499720 + 0x00127> in <19f5e896c781436486db0605884b9d8d>:0 

  at XCalendarApp.MicrosoftGraphProvider.CachedMicrosoftAppointment.ExpandAllOccurrences (XCalendarApp.Common.Timezones.UtcDateTime rangeStartDate, XCalendarApp.Common.Timezones.UtcDateTime rangeEndDate) <0x752d48a6b8 + 0x0042b> in <19f5e896c781436486db0605884b9d8d>:0 

  at XCalendarApp.ProviderBase.CachedAppointment`1[T].ExpandReccurence (XCalendarApp.Common.Timezones.UtcDateTime rangeStartDate, XCalendarApp.Common.Timezones.UtcDateTime rangeEndDate) <0x752d6f13dc + 0x00063> in <486d19f8ca8c4c0d9740bc42f807a0f1>:0 

  at XCalendarApp.ProviderBase.AccountProviderBase`9[TCachedCalendar,TProviderCalendarItem,TCachedAppointment,TProviderAppointmentItem,TCachedContacts,TCachedContact,TProviderContactItem,TAppointmentDbData,TAccountOptions].UpdateExpandedDataForAppointment (XCalendarApp.SQLite.Transaction trans, TCachedAppointment appointment) <0x752d6eabcc + 0x001a3> in <486d19f8ca8c4c0d9740bc42f807a0f1>:0 

  at XCalendarApp.ProviderBase.AccountProviderBase`9[TCachedCalendar,TProviderCalendarItem,TCachedAppointment,TProviderAppointmentItem,TCachedContacts,TCachedContact,TProviderContactItem,TAppointmentDbData,TAccountOptions].UpdateAppointmentAndExpanded (XCalendarApp.SQLite.Transaction

In order to synchronize the appointments with current Exchange servers, the following update would be necessary:

"NTLMv1 disabled for security reasons. If the developers of the app support NTLMv2, it should work again."

I find that with editing appointments I miss some functionality which would make the app a lot more powerfull for me as user.

1. The ability to make an existing appointment repeating does not exist (I need to make a new appointment with all information and put in the repeating option. Especially annoying when forgetting to put in the repeat option)
2. The abilty to change the repeat settings of a range. (I need to delete the current range, make a new appointment with all information and put in the changed repeat settings. Especially annoying when making a mistake with the repeat

Calendar sync error using Windows and on Android.

I am combining numerous calendars - work Outlook, employees Outlook, family Gmail, personal Gmail, wife's Gmail and even another work calendar on Gmail as we transition. A couple of the calendars show duplicate events when I sync certain joint events (manually or using an external app). One calendar should be smart enough to see a duplicate and give me the choice of which calendar displays it, hiding the other. The duplicates often have identical information.

As it is, the calendar looks overly full because of duplicate series'.

I have just launched my own calendar server. This works brilliantly on all my devices, I can access, update and edit all events just fine.

However, I'm having trouble linking up with OneCalendar. Using Davx5 and other apps, the calendar is accessible but davx5 is creating other problems so I want to drop it.

With this, I want to emphasize that I have verified that my calendar generally works on other devices.

However, when trying to add the CalDAV URL to oneCalendar I get the NO RESPONSE error and can't add the calendar to the app. That's a huge disappointment

Same sync error that has been reported by many others.  It's very distracting.  I can't see that anyone has been able to resolve this as yet? Please help, its driving me mad!

Hi,

The app is not showing anniversaries or other events stored with the contacts, except birthdays. It is ignoring other events. Any fix for this will be appreciated. Thank you.

See long subject line.

Need to print Agenda, Schedule(s), Day, Week, and Month views. Adding time or date ranges would be even better. Print in color, b&w, or greyscale with or without Theme backgrounds -- or save each option as PDF.

Print all these options from Android, (iOS), or PC.

It is apparent that the support forums aren't actively monitored by the developers. This is unfortunate and highly disappointing for such a promising app. The app's basic functionality is great, but there in lies the issue; it's basic. It doesn't appear that the developer bothers making any improvements or enhancements such as the moving a repeating calendar event without having to make a copy and delete the old one, adding more customizable reminders, setting multiple reminders, etc. These are pretty basic features in other free apps, and it's pretty disappointing to not see these in a paid app.

As with

Not all Facebook events show up after sync.

Sync problem with iCloud Calendar. "Unexpected end of file has occurred. The following elements are not closed: multistatus. Line 9671, position 1."

I donwloaded the One Calendar app from the Microsoft store for Windows 10. When I click launch, the app opens and immediately shows an error. "An unexpected error occurred in the application. Please close and restart the app." This just continues and I can't open the app. I already tried all the basics, uninstall/reinstall, turn off anti-virus, check Windows updates, reset store, reset app, etc. Any help would be appreciated, as I'd really like to use this app!

For some unknown reason, my 9 calendars disappeared, but local calendar database looks ok, and all accepted invites in "old" folder

I use more than one Calender (Work/Private) with different sub calendars on two accounts (Mcrosost Exchange and 365).

Even if the "work" calendar is "not selected" to appear (still sync is on), all the meeting reminders (alarms) are occuring for it. This makes no sense, as I just want to get them for the selected once (private). So either it should be fixed, or there should be a option like "allow alarms for active calendars". 

Try to sync to yahoo calendar.  This worked several days ago and still works on my wife's android.

I have:

1) cleared cache

2) reinstalled onecalendar

3) deleted yahoo account on onecalendar and readded

4)  deleted yahoo account on onecalendar and readded using newly created yahoo app password

Note that there is no apparent error thrown when adding account, only when trying to sync

I have 3 exchange and one Google calendar account in OneCalendar. One of the three exchange accounts has automatically been set as the default. For some reason, I cannot change the default calendar to either of the other two Exchange accounts (the setting immediately jumps back), only to the Google account.

Is there a fix for this or anything I can do?

Many thanks!

After I tap allow,  it opens a browser screen with no option to return to the app. Then I need to tap back and when return to the app, the account has not been added.