You created a For...Next loop that has the same control variable as a loop it is nested inside. Alternately, you may have created a For...Next loop with an illegal control variable. The following demonstrates the correct structure of a For...Next loop.
Forcounter = startToend [Stepstep] [statements] [Exit For] [statements] Next
To correct this error
Rename the control variable in your For...Next loop to something unique within the scope of the outermost loop.