You might want to read-up for ways of dealing with concurrency in this environment at:
http://www.activevfp.com/dev/dna08.htm
and
http://www.west-wind.com/presentations/aspobjects/ASPObjects.htm
Also, Mike Stewart from MS has done some extensive load testing - see message #627606.

Using MTX is one way to limit the number of VFP mtdll threads.

I would make sure you're setting up your environment the same as the examples. For example:

FUNCTION INIT
SET RESOURCE OFF
SET EXCLUSIVE OFF
SET CPDIALOG OFF
SET DELETED ON
SET EXACT OFF
SET SAFETY OFF
SET REPROCESS TO 2 SECONDS
THIS.cAppStartPath = JustPath(Application.ServerName)+"\"
THIS.cAppName = JustStem(Application.ServerName)
* Set paths (adjust per your needs if necessary)
SET DEFA TO THIS.cappstartpath+'data\'+THIS.cAppName+'\'
THIS.cHTMLpath=THIS.cappstartpath+THIS.cAppName+'\HTML\'

>I am in the process of investigating issues we have been encountering with one of our applications. The application is written in ASP and calls a VFP Com object.
>
>The VFP Com object is written in VFP 6.0 and compiled as a multi-threaded Com object. The VFP Com object does several simple queries to SQL server tables to compile information. The VFP Com object also does a lot of cursor manipulation. The VFP Com object resides on a Web Server.
>
>We have noticed that there are times when the createobject call from ASP hangs when there are several (up to 50) concurrent users on the application at any given time. (With this many users, possibly 3 - 4 calls would be made to the VFP Com object at the same exact time.)
>
>Does anyone have any suggestions as to what may be going on. Is there a limit as to how many threads can be utilized at one time? Is there anything we can do (or any products that we can use) to help pinpoint the problem to make sure that we are not chasing the wrong problem?
>
>Thanks in advance,
>Maria