Sorry! You cannot view this report because you do not have the permission to access one or more module that are part of this report.

To view the report, please provide permission to access those modules in Profiles and Organize Tabs settings.

I have the Professional edition of Zoho CRM and I am the only user. I don't understand why I wouldn't have access to this.

Moderation Update:

The error message, 'Permission denied' will be shown when the Report has data pulled from one or more modules that the user doesn't have access to. Please grant the permission for the modules under Setup > Security Controls > Profiles.

Managing Profile Permissions