Because of a flash error caused by a .swz signature expiring on May 5th an issue has appeared for vSphere Web Client in vSphere 5.0 environment (depending on the version of flash player).

Temporary solution is to replace 7 .swz files (after downloaded delete version number in file name):

datavisualization.swz download
framework.swz download
osmf.swz download
rpc.swz download
spark.swz download
sparkskins.swz download
textLayout.swz download

into each of these locations on vSphere Web Client server (while the vSphere Web Client service is running):
D:Program FilesVMwareInfrastructurevSphereWebClientDMServerworkosgiconfigurationorg.eclipse.osgibundles38datastoreorg.eclipse.osgibundles1121bundlefilerslbD:Program FilesVMwareInfrastructurevSphereWebClientDMServerworkosgiconfigurationorg.eclipse.osgibundles38datastoreorg.eclipse.osgibundles1281bundlefilersl
D:Program FilesVMwareInfrastructurevSphereWebClientDMServerworkosgiconfigurationorg.eclipse.osgibundles38datastoreorg.eclipse.osgibundles1291bundlefilersl
and clear cache on web browser.

If the vSphere Web client service is restarted these steps needs to be performed again.

There is no permanent fix yet.  link_to_vmware_kb