You may see the following error message due to insufficient privileges to Visualforce Pages:
|1||Go to Setup||
Go to Setup and search for Profiles.
|2||Select the User||Click on the profile of the affected user.|
|3||Go to the Access Page||
Select Enabled Visualforce Page Access and click Edit.
|4||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.