Have a look and see if it really makes the new texture 4000x4000 - and not 4000x664625786879806 (something huge) I have seen that happen and it gives me that Overflow error. Not every time, but almost, if I forget to check output size :o/

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.