anyway if you can still play with a workaround:
follow this steps:
1) go here:
https://www.warmane.com/download pick "MoP(old)" and when torrent starts pick ONLY "wow.exe" ( it is 12MB)
2) then rename it into "wow5.4.2.exe"
3) put it inside your MoP 5.4.8 client
and now by using this "wow5.4.2.exe" you can log in on frostwolf until 5.4.8 upgrade, after that you will need to use your standard "wow.exe" already located in your client :)
you have " convert to battl.net" problem? then
1) right click on your MoP folder>properties> disable "read-only"
2) change your realmist into:
set realmlist logon.warmane.com
I guess your realmist was set realmlist logon.warmane.ru, right?