Hard disk space lost after burning CD!?

I burned one audio CD after another using Nero 6 Ultra edition under Windows XP. The first compilation was burned up smoothly, but at the beginning of the second one, there appeared to be an insufficiency of virtual memory, after which Windows terminated the process and started Disk cleanup. After it finished cleaning up files, I burned the CD again using “the same project” option, but when it was all finished, about 500MB were gone!
How can I free up my hard disk space?!
I used Disk cleanup again, and deleted the Prefetch folder, but that’s not it! I even used Disk Investigator, but all I came up with is to disable Hibernation.
Any kind of hlp would be MUCH appreciated,
Best regards,

One post is enough. I’ll close this thread but leave this one open. :cop: