Problem is accessing the sidebar (turning it on).
I have contacted one of the devs of Donation manager, he says he asked someone who used both Donation Manager and Xenporta for a solution. The person said this:
"Check if XenPorta is replacing the default sidebar, if it is and you change it back and the donation manager works then that would be the cause."
Now the question: How do I change back to default sidebar with XenPorta?