go to a different ward and hit "summon retainer". When it shows the picture of your retainer while asking "which retainer do you want to summon" look beneath your retainers name and it will show which ward he/she is currently in. Go to that ward and you should see your retainer (don't try to summon). Walk up to your retainer and click on the retainer to talk to them.
As far as getting the message about not being able to summon your retainer, I think there is a limit to how many retainers are allowed in any particular ward, probably due to fighting lag problems. I get the same message on Karnak server in the Battlecraft ward.
Oh, one more thing... there is currently some kind of bug where you go to into the ward and find your retainer "6 feet under"..... In other words, your retainer is completely beneath the ground and the only thing you can see is your retainer's name.... and the retainer's name is sitting 2 inches off the ground. So go into the proper ward and look carefully on the ground for your retainers name. If this is the case, keep trying to click on the retainer's name and eventually you should be able to talk to your retainer. This has happened to me twice!!
Edited, Nov 22nd 2010 3:11pm by ThinkDeeply
Edited, Nov 22nd 2010 3:17pm by ThinkDeeply