You will need to turn off custom errors in order to get a more descriptive error message. You can do so by following these steps:
- Open your SharePoint web.config file
- Set CallStack="true" in the SafeMode element
- <SharePoint><SafeMode MaxControls="200" CallStack="true"
- Set mode="Off" in the customErrors element
- <customErrors mode="Off" />
Refesh the SharePoint page which was getting an error, and you'll see a more detailed error message along with some stacktrace information.
This operation should not require an IISRESET or application pool identity restart.