"The published message could not be routed because no subscribers were found".. This is the error that every BizTalk developer has seen sometime or the other and most common reason that is seen is either send port or orchestration is not enlisted etc.
I am sharing my experience where i have seen this happening under severe load. I am talking about load of thousands (more than 60K) users per second, Each user was instantiating a web service call(it was required functionality). Everything was working fine for small load but as the load was increased beyond limit (forgot the exact users at that time) we started getting this error.
Resolution:-
After in depth analysis we came to know it was a Host throttling issue. Because the subscribers could not subscribe the published messages (Delivery Throttling). We started to monitor the performance counters and observed that the alloted Memory to BizTalk process was getting consumed fully. We Increased the Process Memory usage to 75% in host throttling settings and the issue got fixed :).
Conclusion - When you see "The published message could not be routed because no subscribers were found" this error at high load one of things you should check is monitor the performance counter for process momory usage (obviously first step will be to check whether the subscribers are enlisted or not :).)
Throttling details have been very well explained by Tord at http://biztalkadmin.com/biztalk-self-throttling/
& on MSDN at
http://msdn.microsoft.com/en-us/library/aa559893.aspx
I hope this post might be helpful If anyone of you ever face this issue anytime.
- Have a Great Time
Shailesh Kawade
