[WarLion]

the version 2 have a diferent name product when you install the v 2.5 you still have the other version using the files in include/functions_wl_online_offline.php

you last version that you use was the 2.0 but you dont uninstall the old files i guess you still have the include/functions_wl_online_offline.php file in your ftp when you upgrade to 2.5 you make two products with a diferent name causing call the same funcion at the same time thats the error
Cannot redeclare fetch_online_status_mod() (previously declared in
cuz you already have it declare

if you have the /functions_wl_online_offline.php on you ftp is now safe if you delete is not need it anymore

actually was my mistake for change the product name betwen the vercion 2 and 2.5 , i change that cuz i start all one more time to make the new version 2.5 and imake a mistake with the name and put a diferent.
and i guess you download the vercion 2.5 when a editing this post and cause a misundertood sorry for that
and is strange that you cant go to your admincp cuz any file , plugin or anything is calling over admincp , cuz i have this kind of errror hundred of times when i start the prroduct
and my admincp alway was active and woring fine
the only thig i can guess is that you trying going to your admincp via forum link insted the forum/admincp/index.php adress

now if you upgrade from 2.5 to 2.6 is not problem cuz is the same product name but if you upgrade from the 2.0 to new one you have to delete the files and uninstall the older version first