com.htc.bgp errors have been coming up for years, Google it and you will find plenty of fixes.
The most common causes are an error in calendar storage, or Facebook syncing. Go to settings>apps>calendar storage then click on clear data, also do the same with the calendar app itself and gmail while you are there. Some users have reported the error if they have a non-alphanumeric character in their facebook user name, such as an apostrophe. The only fix for that appears to be logging out of Facebook and turning off syncing, or changing your user name.
There may be other solutions you can find if these don't work.