I keep getting this error message when I create a message or delete a message and rebuild the site.
MT 3.0D
Perl 5.6.1
"
DateTime/LeapSecond.pm did not return a true value at extlib/DateTimePPExtra.pm line 5. Compilation failed in require at extlib/DateTimePP.pm line 5. Compilation failed in require at extlib/DateTime.pm line 42. BEGIN failed--compilation aborted at extlib/DateTime.pm line 44. Compilation failed in require at lib/MT/Template/Context.pm line 1302 "

I think something happened causing the LeapSecond.pm to not be uploaded to your server properly. I'd suggest re-uploading the [mt.cgi dir]/extlib/DateTime/LeapSecond.pm file to the server (making sure it is uploaded in ASCII mode).