I've got my main form, with three sub forms. They are all linked to customerID. Now, two of the subforms are working fine, with the exception of the third which gives me "This expression is typed incorrectly, or it 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". What?!! There's only seven fields in the table with the customerID the link and productID the primary key. Please help!!

The only time i have ever seen this message appear is when you have a calculated field based on another calculated field.

Try re-writing the formula for the tex box checking you are using the long locations for the fields.

I thought I read once where access only supports two subforms in a form... maybe that is the problem.

I've created a form containing 9 subforms without problems, so that's not the reason. Is the subform based on a query, may be your problem is there.
HTH