What you're having a problem with is a folder called the "dtt" folder most likely. This contains five images that the game uses for the maps wiz05 and DC2, so without them you can't get in.

First get the 'official TT mod pack' as posted by Regeant x. Its about the top of the list in general forums. Follow the directions contained in the folder once it is downloaded.

This should clear your problem, the TT mod pack has the 'dtt' folder on it, so if you followed the directions correctly you should have put it in your missions folder.

To get to the missions folder do the following (mac): control click on the think tank's icon and select "show contents"

Once inside click on the folder 'game'

From game click on 'data'

From data click on 'missions'

These are the terrains, this is where you want to dump all the files in the TT mod pack file into.

Make sure you put the 'dtt' and 'demo' folders in there too. TT automatically downloads new terrain files if you let them load long enough, but it's much faster just to get them all at once. However it does not download the dtt folder, so you get the 'invalid pack response.

This should solve your problem.

Post if you need help

Thank you for your help. It fixed the problem. I appreciate you taking your time to help me.
Hyde

Glad that I can be of some use around here