Well I certainly hope you don't lose your job! Was the email personal? You said you interpreted it. so was it more of a generalized message about your efficiency levels or a specific account of issues in your performance, when they occured, etc?

I ask because different companies have their own ways of "motivating" their employees per se, and they could be sending similar messages to many employees as general warnings or "motivators" from their perspective anyway.

Hopefully they are just bluffing and you will continue to get projects.