Some times QuickBooks generate error while opening company files which says that your company files is corrupt or damaged. In this situation you need to first verify your company data and then rebuild all company data to correct it. QuickBooks provide a company file diagnostic tool which help you to verify and rebuild your company file damaged data. You can repair QuickBooks file with this utility.

Purpose of Verify Utility:

• It verifies each transaction and find incorrect one.
• It records details in Qbwin.log file.
• Find the list of damaged items.

Purpose of Rebuild Utility:

It repairs damaged or corrupt QuickBooks company files.
It updates total incorrect state data.

Here are the following steps written below to verify-rebuild process with company file diagnostic tool.

Steps to verify data:

1)First of all close QuickBooks and reopen it and create a new Qbwin.log file.
2)You need to be sure that all company file and QuickBooks windows are closed for this go Window > Close All.

3) Go to File > Utilities > Verify Data and data verify process will be started.

Steps to Rebuild Data:

1)First step to rebuild data is similar to verify data, just you need to be sure that all company files and QuickBooks windows will be closed, to do this go to Window > Close All.

2)Now start rebuild process by File > Utilities > Rebuild Data.

3)If any message regarding backup pop up then click OK.

4)At the bottom of the Save Backup Copy window, click Save.
5)At the completion of rebuild process click OK.
6)Now close all company files and report it to refresh whole list of files.
Choose File > Close Company. 
Choose File > Open or Restore Company. Then select Open a company file and click next.
7) Now click on company file and click Open.
8) You need to run verify data utility again.
9) After verify data process you will get message “QuickBooks detected no problems with your data.” It means your damaged QuickBooks company files have been updated.