Nimbostratus
CirrusHi,
I'm glad that you managed to solve your issue by changing the Source Address Translation. I thought it would be a good idea to post some of the issues that I have experienced and some troubleshooting steps that I have identified, so if somebody reads this question and has the same issue they can troubleshoot it. If you disagree, I'll remove the answer.
I always like to check the statistics for that Virtual Server once it comes down to troubleshooting of this issue. If it is getting Inbound traffic but no outbound that usually indicates the issue with Source Address Translation (the issue that you have experienced).
If it is not getting any kind of traffic and you are still able to ping it, in my experience this can indicate IP address conflict in the network. You can check this by changing the IP of the Virtual Server and trying to ping it again. If you are able to ping it, then probably something else is using that IP.
If it is getting both inbound and outbound traffic but you are still not getting a proper response using curl or some other web client then it might be best to look into pool statistics. If the pool is not getting any traffic, check that the pool that you want to use is set as default pool on virtual server.
If the pool is getting some traffic, then check the traffic of it's pool members. If they are getting some traffic but you still are not getting a proper response, try to access them directly. It could be that the issue is on the node it self, in this case you might want to consider creating a custom monitor for your pool members if they are not already marked as down.