You may see the following error message due to insufficient privileges to Visualforce Pages:
|Go to Setup
Go to Setup and search for Profiles.
|Select the User
|Click on the profile of the affected user.
|Go to the Access Page
Select Enabled Visualforce Page Access and click Edit.
|Make the required changes
In the Available Visualforce Pages column, select all options that start with iv.InsideView_ and click Add.
Ask the user to refresh the page; the issue should now be resolved.