cubase vst 5 problem

Hi, I hope someone can help me. I’ve been using an old Cubase vst 5 for a while but my hard drive went pop. I reloaded windows xp on a new drive and then reloaded Cubase vst 5 on the disk as before. All seemed to be fine opening the program to check, but when reopening for the second time to use, it, I got an error message saying something about unable to open “getinfo”. I tried installing the same Cubase vst 5 software on my partners pc running windows 7. loaded ok opening the same but on reopening a few minutes later, the same error message appeared. Can anyone help, as I’m getting depressed and frustrated.