The Blender 2.5x series uses Python 3.1. Any script that is outdated will not work in Blender 2.5x. If you scripted anything using the “old” scripting language, it may not work. Also, many features in Blender 2.49 have yet to be implemented…
But, if you are just pressing “P” and there isn’t any game. That is an entirely different problem. Also, the game engine uses Python 2.something… Uninstall, and reinstall Python 2…, not 3.1.
I don’t know if this will help you, but it helps me.
I had this problem for a while and eventually figured out what it was.
Turns out, Blender 2.56a does NOT like it when your save file is in a folder with symbols on Windows 7. (That includes temporary and .blender).
I saved the file I was working on in something like:
c:/blenderprojects/thisproject/
And it worked fine. As long as the folders don’t have “.” or something.
Does moving the save file to a folder with no special symbols help?
Edit:
If it helps anyone fix the bug, I think I narrowed down the problem:
When I open this file:
C:/users/Leopardson/Desktop/asdf/fdsa.blend
Blender says:
C:/users/Leopardson/Desktop/asdf/fdsa.blend
And it works fine.
When I open this file:
C:/users/Leopardson/Desktop/£/
Blender says:
C:/users/Leopardson/Desktop[]/£/
What I did is I installed blender in “my documents”. It did not work very well when it was in “program files” or in “program files (86)”.
I’m using windows 7 myself, so it should work.
Edit: Also, just to make sure you don’t have many problems, run it in compatibility with windows vista. I don’t recall doing that, but I think I did it (given that I faced problems at the start).