"Invalid property" after "Clear Form"

Hi - My VBA project is an insurance premium calculator.
It works except for one REALLY annoying glich that I can not work out.

If I start the calculator from scratch it works fine.
Then if I hit the "Clear Form" button (this clears all the fields on
the user form I created)
and then try and use it again I get an error that says "Invalid
Property"

The "Invalid Property" error is incorrect. I have tested it at least 50
times and no matter what I put in the field it still doesnt work.

Can I email the file to someone to have a look at?

This would be greatly appreciated as this is the only thing left to
fix.

Thanks in advance.
Bernie

PS this is NOT a simple "Invalid Property" notification. The property
entered is correct. However this message still appears.