As long as your computer can handle the processing, you should be able to connect 3 (or more) webcams to a computer. If your computer wasn't able to handle the processing, it would just use a lot of CPU %, it wouldn't display that error.
We've never seen that error message before and no other user has reported it before. Please send a screenshot of the error message to support@skjm.com. Refer to this forum thread in your email.