A Brother MFC 665CW printer was setup to a PC via USB, but every time the scan to email function was used, the PC would generate:

The command line argument is not valid. Verify the switch you are using.

After some digging I find the solution at: techyForums

Which basically pointed me towards downloading an update/patch for Brothers Control Center 3 at: Brother patch for CC3

After that it worked well.

Except I now needed to install CC3 onto 2 other PCs, together with installing the patch another 2 times… fairly time consuming. 🙁