Theme / site failure for

Hi is a domain mapped network subsite on my network.
I’ve installed a new theme I want to use on this site ‘Bimber’, but it seems to be conflicting with what was the previous theme ‘Gowatch’. I’ve disabled that at the network level but it still doesn’t work.
When I go to the top menu ‘Theme options’ it gives me a ‘you’re not allowed to access this section’ failure message.
The Bimber theme support guys say this is a leftover from the previous theme, not their option.
How can I resolve this? I have enabled Support Access.
Thanks, Neil.