HELP - FORBIDDEN you are not allowed to enter document after admin-login

Hi everyone,
i realy hope anyone can help me … i am running version 4.8.4 and everything was fine, the shop was running for months … than, without any big change, i tried to login today and a big problem appeared. First after login as admin everything looks fine. But as more i click into details, no matter where, i get the message “FORBIDDEN - You dont have permission to access this document!” … wow, if i reload the admin-page i get this message only. I have to clear cache and restart browser, login again, but the problem is still there. I click on a product, and insteat of editing the details the error disappears. one more click and even the menu on the left side disappears, reload after that and everything disappears and i got the errormessage only. why?

so please … can anyone help me with feedback? thank you so much … i dont know what to do now …

after writing this post it worked out for view minutes before the problem appeared again. what can be the problem? anyone knows or ever had this problem too?

System-information is all green, ok.

but when i am running the diagnosis it gives me a warning on top:

Warning: disk_total_space(): open_basedir restriction in effect. File(/) is not within the allowed path(s): (/…/domain/:/tmp/) in /…/domain/httpdocs/eshop/application/models/oxdiagnostics.php on line 495

Warning: disk_free_space(): open_basedir restriction in effect. File(/) is not within the allowed path(s): (/…/domain/:/tmp/) in /…/domain/httpdocs/eshop/application/models/oxdiagnostics.php on line 505

can this cause the problem? i am web-developer, but this lines dont tell me anything what it means and what it is about … hmmm

It seems to be a chache problem, but how to fix it ???

Your hosting provider changed something on the server. Please see what was changed with the PHP variable open_basedir.

Cheers

thank you, i am waiting for answer from my provider, lets see what he says … thank you so far. i will post the answer asap i get it.