You can use the Rebuild Utility to rebuild files if there corruption on the file. 

Follow the steps on the below video to rebuild a file. 

Refer to article How do I process a backup Sage 50cloud Pastel Accounting?

If for any reason you cannot process the backup, you can create copy of the company folder by following the steps below:

• Close Pastel.
• Open the Pastel installation folder which should be located under the C drive or the drive where Pastel was installed. If the data is on a different location, you can go to correct data location.
• Right click on the company folder and select Copy.
• Go to the desktop, right-click and select Paste.

Please ensure that Sage 50cloud Pastel Accounting is closed on all machines when following these steps.

To rebuild the file, please do the following:

1. Open the Pastel installation folder which should be located under the C drive or the drive where Pastel was installed
2. Double click the application file Rebuild32 to open Rebuild Utility as shown below

3. Click OK on message as below.

4. Select your C drive (or the drive where your data is located)
5. Double click on folder where the data is located in the second block
6. Double click on the company folder 

7. In the last block, double click on the relevant file(s) and click on Rebuild. For example in the screenshot the file to rebuild is ACCTRN.DAT

8. Once the rebuild is done, click on View as shown below and ensure that all files have been recovered.

9. If all records have been successfully recovered, you will see screen as below with the same number of records on contained and recovered.

If you receive a Critical Error 2 or any other error on the rebuild, we recommend that the client restores another backup before they had the issue and reprocess all transactions captured on Sage 50cloud Pastel Accounting and POS after the backup was done.

Refer to article How do I restore a backup in Sage 50cloud Pastel Accounting? if needed.