If when clicking on the Estimating button from the main menu and you get an error which kicks you out of the program.

If running locally log back into the program.
If running in the cloud,  close the session WAIT 1 MINUTE before trying to log back in (this will allow the system to reset)

either method you must then do the following:-

v12 
Click on Setup - Company Setup
v14
Click on Settings - Global Settings

Then click on "Upgrades and Integrations"
Under "Repair Files",  look for "Estimating"

Click on OK at bottom left,  your estimating module should now open correctlyIf however you still have issues feel free to contact us or open a support ticket