Since you have other filters that are working fine, you must be using similar code and, for all intents and purposes, know what you're doing.
My suggestion would be to try putting the filter in a query and make sure you're getting the syntax for your Me.Filter value correct...
Go to the Quantity field in your query, enter the criteria >0, change to SQL view of the query and extract the string that follows the "Where" clause in the query. It might be as simple as needing a space between > and 0.
You might also try Me.Requery instead of Me.Refresh.
Randall J Weers
Membership Vice President
Pacific NorthWest Access Developers Group