Hi koder2,
It seems to be the same problem. Error message seems to vary between different versions of vSphere. The fix will be available in the next version of PowerCLI. Currently a workaround is to give the user at least readonly access to the host the VM resides on. If you cannot do that there is another workaround - use Onyx and reuse the script that vSphere Client uses to update the memory size. This requires a little bit deeper knowledge of PowerCLI, but I hope you know what I'm talking about.
Kamen
PowerCLI team