CRM by default tends to throw a General error for any error that occurs. If you need to have a more specific error, enable DevErrors in Web.config.
To do it do the following:
Step 1: Goto the CRM Web Server to the Web Installation path.
Step 2: Open the Web.config file
Step 3: Change the value of DevErrors Key to ‘On’
Step 4: Save the Web.config file.
Now CRM should show up more specific errors.