invalid date error when posting event to Calender

[tty456]

When posting an event to the Calender it fails with "an error occurred" "invalid date" unless the 'all day' option is ticked, nothing appears in the logs either in smf or webserver that I can see.

If posted with 'all day' ticked then it creates it with no issues.

The forum was an upgrade to 2.1 RC2 from 2.0 and has gallery lite mod and tiny portal mod (we changed to Tiny portal from simple portal as wasn't supported in 2.1 )

I tried a fresh clean install of 2.1 RC2 on a test domain and Calender works as expected, so then added the two mods above to see if they broke it - but it still works with them added.

If I manually add a start time, ends time and timezone into an existing event in the Db smf_calendar then it shows correctly in the Calender!

Not sure how to find the cause when nothing in the normal logs - any help or pointers appreciated!