UBB.threads PHP Forum Software Community Forums UBB.classic UBB.classic 6 Support CGI Error

I got this error when sending a mass emailing from the members list area of the control panel. It was going to about 1000 members. What does it mean? How do I know if they were all sent? How do I know WHICH ONES got the email? Thanks

Here it is:

CGI Error
The specified CGI application misbehaved by not returning a complete set of HTTP headers. The headers it did return are:

THAT IS ALL THERE IS TO IT.

I forgot, I am using the new beta version 6.7.0