While saving the data it saves two files..one backup file and one original. E.g if you are trying to save 50mb file you need 100mb free space. When i used to get this error i have tried saving the file in local folder instead of on server. File gets saved and then i used to copy and paste the file from local user folder to server location.

Sometimes CATIA file has got some internal errors. I have also tried performing CATDUA on the file.
Go to file desk. Select your CATPART and run CATDUA. Sometimes it also solves this issue.