When I open a form I get a diaglog box that displays

tablename.field name
Enter parameter value

Why is this happening? How do I fix it?

This is happening because Access cannot find the field and therefore thinks that it is a parameter.

Check the syntax on the form very carefully.
It's probably wise to delete the control that is causing you a problem and recreate it from the field list.

Hope this helps

This is a common problem. If you have done any work to your underlying table after the initial creation of your form, probably more specifically to the field that is being referenced, you will get this error. As the previous reply by Former, you should delete the control from your form and re-insert it from your field list. All should be well.
P.s. also note that if you have reports linked to this table as well, you may have the same error occur there. The fix is the same...delete and replace.