dlane's post above put me on the right track to a fix in our environment, so thanks for that! Ultimately I had a service ticket go all the way to VMware Engineering to verify what was wrong and nail down the process to fix it, but this was the key. Our vCenter server had two NICs, one of which is on a private non-routed subnet. The URL to the statsReportExtension.xml file was pointing to the unroutable IP instead of the one it should be, so clients couldn't reach it. Manually pointing a web browser to the URL with the correct IP can confirm this.
So, fixing this is a two step process. First of all, find the offending XML file and correct the IPs in it (should be like 3 instances, one in each stanza).This will point clients to the right data once they get the correct XML file. You should be able to find it under Program Files\VMware\Infrastructure\VirtualCenter Server\tomcat\webapps\statsreport\extension or something similar. Confirm the correct values by manually pointing to the URL with correct IP from a client system.
Second, you need to correct the values in the vCenter DB that tell the clients how to reach the XML file in the first place. You need to stop the vCenter service and Web Infrstructure Access service first. I also advise a backup of the vCenter database. Use a SQL query editor to connect to the DB and look at the entries in the VPX_EXT_SERVER table. Find the entry with EXT_ID=com.vmware.vim.stats.report, and correct the IP address in the URL column - don't change anything else, just the IP in that one entry. Save the changes and restart the vCenter and Web services. This should now correctly point clients to the XML file. Confirm that Perf Overview still works OK on the server itself (open VI3 client to "localhost"), and if that's working, see if it fixes the plugin on the client side as well by opening a new VI3 client session to your server. You should see that the Performance Overview tab appears when you have a Host, VM, or Resource Pool selected. You should NOT need to go to Manage Plugins and download anything, it should just be there when you start the client and select the inventory item... Trying to download the "report" plugin is NOT going to work and will result in the "Invalid URI" error.
If you're still having problems, it's probably a different issue... try some of the other fixes/articles already linked here, or open a Support case with VMware. Good luck!
