Error message repeating

My eM Client on my PC and Google calendar on my android (samsung) aren’t syncing correctly and tasks do not move to the phone at all. I keep getting the following error but don’t know how to correct it.
[Google Calendar]Uploading item(s) to folder ‘’ failed due to the following error: Value cannot be null. (Parameter ‘value’)
Any thoughts. Would like to sync all my contacts from eM client too.