Wirelessly posted (htc Pocket PC: Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 8.12; MSIEMobile6.0) Sprint T7380)
I agree. Try another backup app. Maybe revert to an older backup if you have it? It sounds like something in that file is corrupt. You could attept to import the calendar backup file into a viewer of some kind to try to fix it.