Incompatibility between R701 and R65x - HELP!

I have made some design changes to standard Notes Calendar form in R701. It works perfectly there, but accessing the same database from R6.54 is not working - I cannot enter the Subject field, or tick any of the option boxes above that line. It’s wierd - like the top section of the form is blocked off. Everything else works. When I open a new meeting in the calendar, the cursor is positioned in Subject, and I can type, but if I click out of the field, I cannot get back in.

Help me please.