FAT to NTFS conversion

We are converting all of our NT workstations to NTFS volume. On most of machines, the process ran smoothely but on this one machine, it keeps returning the error “insufficient disk space”. The free space on that C drive was originally about 750 MBbut even after I freed it up to 950 MB, it returned the same error. On the other machine, there was only 800 MB on C and there was no problem. Please advise if anyone has ideas. Thanks.