The issue is caused when you do not have the appropriate privileges to write to the report directory in the Metastorm installation folder.
Please follow these steps to resolve this issue:
1. Go to \..\Metastorm\BPM\Web\app_data\XtraReports\Filestore.
2. Select this folder, and right click > Properties > Click on Security tab.
3. Select Users group > Click on Edit Button > Allow write option by clicking checkbox for Write.
4. Click on Ok.
5. Now open a command prompt, and move to above location (\..\Metastorm\BPM\Web\app_data\XtraReports\FileStore).
6. Run following command:
icacls . /setintegritylevel l