Using Remote Assistance in Windows XP

We have just gone to Windows XP for our new pc’s.
For troubleshooting we were using pcAnywhere.
But on these machines we tested the remote assistance to ensure that we could take over the machines and assist users.
The tests worked great but today I am trying to assist a user at a remote site.
I have taken control but am unable to do anything.
I can see what the user is doing (which is great) but I need to be ‘in control’ so that I can take care of the problem.
Any ideas?
I have added our admin account to the remote tab in System in control panel but still no luck.
HELP, please and thank you,
Mary