VBA Filer Error

On random VBA projects I end up with Filer errors. Nothing changes in how I insert blocks from routine to routine, and if I open the editor and retype the file name, the routine works the vast majority of the time. I can't think of anything that would account for such arbitrary errors. We're running 2007 on XP Pro. Anyone have any ideas?

Thanks, Will

i.e...

Dim blockTSheetObj As AcadObject
Set blockTSheetObj = ThisDrawing.ModelSpace.InsertBlock(dblOrigin, "tsheet.dwg", 1, 1, 1, 0)