2007 Calendar unable to use custom form created in a previous vers

We have a shared calendar with a custom appt form created 3 yrs ago in a
previous Outlook version. After installing Outlook 2007, receive msg that
the 'object cannot be found' when trying to create a new appt. The form can
be fully used in previous Outlook versions. Previous appts can be
viewed/edited in Outlook 2007 but not created. I've cleared the cache and
deleted the forms from my local pc. I've modified security settings to allow
script in shared folders and installed all updates. Any ideas on what to try
next?
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Thanks, Valerie