Can't create HTTP response output file projects/project URL/application name.exe
From BOINC Wiki
This error can happen when:
- the application mentioned is being actively scanned and blocked by anti virus. The AV may have flagged a warning as well, or is waiting for a response from the user about what to do with this file.
- there are permission problems after the BOINC Data directory was moved to another place and BOINC wasn't reinstalled to fix the permissions on the folder.