If you have created any fixed assets under the tab, you need to delete them first before being able to turn off the tab.
I have sub accounts under Fixed assets that were there before. I have nothing under the new Fixed assets, at cost and Fixed assets, accumulated depreciation that appeared after activating Fixed assets tab, and there are no posting to these two accounts.
In Control accounts I can see there is a 1 for each account though.
Go to Fixed Assets tab. Is it empty?
No! There was something I had started to create. Removed and now I can also remove the Fixed Assets tab.
Thanks, all is back to normal, even the screenshot I posted in my last comment the account I had issues with is back with a positive figure.
Thanks a lot @lubos