IIS4 FTP refuses connections

I am running IIS4 with SP6a and IP directory security. I am getting clients that cannot connect. In the event log, I am receiving Event ID 8 with the following error:

FTP Server could not create a client worker thread for user at host . The connection to this user is terminated. The data is the error.

I have the appropriate IP in directory security as being able to have access. Is there anything else I need to do? Thanks for the help.

Gary Carmichael
MCP