Symptom
You do not have permission to use this report in Report Studio

Problem
When click report to open in report studio, the error appears.
  
Cause
The report studio capability on the package associated with the report was set to Deny or not set at all.  
  
Solution
Grant the Report Studio capability to the Package associated with the report.

Steps:
1. Click the Set Properties icon for the Package
2. Click the Capabilities tab
3. Check the "Override the capabilities acquired from the parent entry with" box
4. Add the user/group/role and set the Report Studio capability to Grant.