Halo PC

Okay now, I have Halo for the PC. The first one. Considering that I just put the Halo folder that is installed in my original PC to my Flash drive. I went to my friends house and he has a limited account, but he can still do pretty much everything except install things and go to explicit websites. So I execute the Halo program and play for the first time and create a profile then when I'm done I quit. I come back the next day try to execute and it says having trouble reading from the my documents folder. My friend doesn't have a second hard drive and I went to the my games folder and then clicked on the halo folder and I try deleting it, but it says that the file is in use. I end all processes of Halo from Task manager. Afterwards I try again and it shows the same problem!

Please help!