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Descent 3 Error
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Error: Unable to set temporary directory to: "C:\Program Files (x86)\GOG.com\Descent 3\custom\cache"
The directory is in use, please use -tempdir to set a different temp directory
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OK
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Then it won't let me play.

Hm, I can get around the error by deleting the content of that folder, however when I run it it just minimizes and does not play, can't seem to find a way around that yet.
Ah ok got it
Had to disable visual themes and stuff like that.

Gah I am having the same problems...
Asus P5q3 deluxe 2.33 Intel Quad
Radeon 4850x2 Sapphire

Did you ever find a fix for this? I've been getting the same error

Look in the custom\cache folder for a file called .LOCK and delete it. That should remove the error about the temp directory.

You can also disable visual themes and stuff like that under compatibility, at least that's what fixed it for me.

I got this error. I have win7. it's a user priv issue likely.

I right clicked and selected "run as administrator", then allowed on the popup box.

had to reset my settings but they stayed for when I launched without that and havn't gotten the issue again.