You rebuild a file when there's corruption on the file.

1. Make a backup. 
2. Hold Windows key + E on your keyboard to launch File Explorer.
3. Go to your local C drive and open the Pastelxx/Xpressxx folder.
   • Where xx represents the version of Sage 50cloud Pastel you're running
   • Example: Pastel19 or Xpress19
4. Double-click Rebuild32 and click OK on the message.
5. In the small box, select the drive where your company folder is.
6. In the second box, double-click the company folder.
7. In the last block, select the relevant files and click Rebuild. 
8. Ensure all records are recovered by clicking View.
   

 CAUTION: Restore an older backup of before you received the original error if you receive a Critical Error 2. Reprocess any missing transactions. 

Refer to the article Restoring a backup.