When in the VB window, click on the binoculars and type the varable name. Then search and access will scroll through and highlight each occurance of the word.
Also remember to select 'current project' to search all the code.
Eventually you should come across the Dim statement (Dim yourvariable as String (or whatever))
Viewing each instance you will eventually make sense of the problem and find the source of the variable value.
Dave