this is a problem that happens when you use the same name for a column in 2 tables.
I recommend to always use unique names for your columns.
the naming convention that i like to use is to preface the table name for the column:
productCategoryID - relates to categries.categoryID
by using unique names, you will never run into the ambiguous column name error.
If you must use the same names in your columns, then you will need to edit the data assist search criteria definition to include the table name, if you need assistance with this, send a copy of the page and i can show the code to change.