can you post the first two lines of your csv to pastebin so we can have a look at your header and a sample post?
(please open your csv in Notepad or similar, not Excel)
my suspicions lie with the date format being spewed out from Excel.
I have this set to a custom number format in Excel
dd/mm/yyyy hh:mm:ss
My limited PHP knowledge tells me that the import is looking for a dtstart/dtend in the format d/m/Y H:i:s (lines 483 and 489 of Class.EM_ImpExpImport.php) see php date formats
yours is perhaps producing a csv with m/d/Y?