Error on Form Open

[Guest]

I have a form with a subform that consists of 31 list boxes that are set up
like a calandar Month and year based on combo boxes also on subform. This
form worked fine until I put SQL (quite complex and lenghty) in the "Row
Source" of the list box. This populates the list boxes with reminders from
an events table.

It all works fine when the form is open, but If I put the form in Design
Mode then Form view or close it then open it I get an error 31 times"
"The expression is typed incorrectly,or is too complex to be evaluated. For
example, a numeric expression may contain too many complicated elements. Try
simplifying the expression by assigning parts of the expression to variables."

Can this be true if the form works fine when it is open already. Any other
Ideas?
Thanks in advance

 

[Guest]

I'm Sorry,
It took most of the day, but I found that some of the variables in the SQL
could evaluate to "Null", resulting in sporadic errors. I'm still working on
the fix, and only assume this was the problem, so still would appreciate
input if any thing else comes to mind.