Can't add Device. Get "Device already present in the System"

I'm getting "Device already present in the System" when I try to add a new virtual vmware host. I tried before and get some weird error and now I get this error.

The knowledge base on this, http://www.manageengine.com/network-monitoring/kbase.html#kbase56 is way out of date and doesn't work.

License Type	: Essential
Build Number	: 11300
Latest Version	: 11300 [ Details]
Expires on	: Never
AMS Expires on	: 09/15/2015 12:00:00 AM EDT
Maximum no of Devices	: 50

OS Name & Version	:	Linux, 2.6.32-220.17.1.el6.x86_64
OpManager version	:	11300 (64 Bit)
Working Directory	:	/opt/ManageEngine/OpManager
Database Type	:	MYSQL
Total JVM Heap Size	:	239 MB
Used JVM Heap Size	:	176 MB
Free JVM Heap Size	:	62 MB
Load	:	1.91 polls/sec
Thread Count	:	194