"You already have a pending match."

[DrBalefire]

Error everytime i try to invite to a group, or when someone tries to invite me, relogging does not fix this.

[Iulica]

That happens, if you, or the one who you are trying to invite is in queue for something ( rdf/bg etc. ). It is a bug since some time now, next time leave the q or tell him to leave the q, when you want to invite.

[DrBalefire]

except i have been in no que when this happens, especially after relogging, and it still persists

[ludovicostone]

The most annoting bug after the "You have exited the Wintergrasp Battle"

[DakMonkey]

leave group, logout, login. This has solved it for me every time so far. /reload isn't enough, but good ol /camp is.