If I think what your are saying ...
you have two areas that are the same type of geometry, but only one will fillet?
Try making the fillet much smaller to see if it works. If it does, your fillet won't work because of geometry constraints.
Can you show a pic of the areas?
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06 ctopher's home (updated 10-27-06)