Try the info below: It is from here on page #2
http://answers.microsoft.com/en-us/...0/564d09fb-3e5b-49ef-ae2f-3aa6d7e7f1ac?page=2
I believe I solved this problem. Please verify for yourself by completing the steps below and report if this works for you or not.
First, lets remove the Mail and Calendar apps.
Open PowerShell by doing a search for powershell in Cortana or in Search Bar.
Right click on "Windows PowerShell desktop app" and select "Run as administrator".
Copy the following line:
remove-appxpackage microsoft.windowscommunicationsapps_17.6120.42011.0_x64__8wekyb3d8bbwe
Now right click in the powershell window and it should auto paste into the powershell window. Hit enter.
Once a new line prompt appears in powershell you can close it, we are done here.
Now open File Explorer, previously windows explorer and go to the following location:
C:\users\Your User Account\AppData\Local\Comms
You may need to enable show hidden files and folders in the Folders settings from control panel.
Delete All the files and folders from within the Comms folder, there is one folder "UnistoreDB" that can't be deleted but there are some files in there that can be, go ahead and delete the ones that can be.
Mainly you want the file CalendarCache.dat removed, it is in one of the other folders, but it doesn't hurt to clean out all files and folders there also.
If you do NOT remove the Calendar App before or after removing "CalendarCache.dat" I discovered on my computer the Calendar App won't open anymore even after reboot, which is why we remove it completely then reinstall just for the purpose to verify if this process worked for you.
Ok, now go to the Store app and search for "Mail and Calendar" and reinstall the app.
For me I no longer have any reminders set. Now go to Cortana and set a new reminder. Once done go to Calendar and see if it is there. You still can't edit or delete from the Calendar app. Now go back to Cortana and delete the reminder. Go to Calendar App and it should be gone.
This works for me. Let me know if it fixes your problem too.
Now if you want the Mail and Calendar app removed completely just go through the powershell process above again. For me though since it seems to be working I just kept it installed.