Geoprocessing tool COMException: Exception from HRESULT: 0x80040304

[AGheidian]

Hi, I have geoprocessing tool which opens a MXD template file to make PDF out of the map, using Export method.

Intermittently this tool throws error  COMException: Exception from HRESULT: 0x80040304

I am releasing COM objects but still sometimes throws this error. This is snapshot of my code:

Any ideas?