There appears to be a conflict between Apple Network Administrator Toolkit or Apple Network Assistant and the FaxSTF software.
To resolve the situation, follow these steps to move the Network Assistant Startup extension from the Extensions folder to the root level of the System Folder:
1. Open the System Folder.
2. Open the Extensions folder. Both folders should now be open and their windows visible.
3. Drag the file named "Network Assistant Startup" from the Extensions folder to the System Folder's opened window.
4. Restart your computer.
The error message should be gone and Network Assistant will continue to function normally.