Did you try restarting the instrumented JBoss process? If it doesn't help and you get the same error messages again try restarting the collector if that's feasible for you.
We had a similar issue a few days ago and above steps helped.
Do the following steps:
it is taking too long to connect to your collector. I can think of 3 possibilities:
1) the collector is not powerful enough to service the request
2) the network latency is too high.
3) if you are using collector groups, you might have multiple network interfaces on the collector and some of them are not reachable from the agents. Explicitly defining the listen address will fix this.
For point 1), I saw this recently with a collector running on a VM deployed on a server which was totally saturated.
For point 2), Don't forget that the collector and agent must be "close" to each other (ideally on the same subnet and no firewall in between).
For point 3), if you do have multiple IPs (public , backup or management network for instance), specify the public IP in the advanced screen of the collector configuration screen under override external address.