Apologies. Here's the complete thing.
I have a query involving multiple tables and sub-queries. Only the equipmentID field is multivalued and using a lookup from another table (containing equipmentlist). It is then indexed along with the customerID.
This query is working fine in query mode. The expression I posted is the access generated filter for displaying a "customer" who can use both A and B (both are in the multivalued field). I copied from the form filter property. Actually, access had put an "OR" between A and B but I changed it to "AND".
Now, the problem comes when I am using it as a subform in a form which lets the user select the filter options using dropboxes and checkboxes (A and B are checkboxes").
The options are converted to a string joined by AND and this is where I am facing an issue.