Exactly how do you call the external batch file?

Could you post a minimal, working example? Maybe it has the same behaviour even without using Tk? Try that and post that minimal (but complete in the sense of "you can run it") code as example.

Since there are quite a lot of ways to call an external program or batch file on window, at this point we can't even take a guess on the exact nature of the problem.

BREW /very/strong/coffee HTTP/1.1
Host: goodmorning.example.com

418 I'm a teapot

In reply to Re: Par Packer - gui option problems by cavac
in thread Par Packer - gui option problems by Dirk80

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