Problem:
I tried to write VAG MED17.5 TC1766 modified file with Foxflash, but failed. It says error incorrect file. OTP sector not writable.
Solution:
The message says it all, the file you are writing contains information for the OTP area, either the file has been modified wrongly, does not come from the Ori file, or address offsets have changed through a solution software used to modify the file. If you write Ori back without problem then problem is your file. Do solution in Winols from Original file.