Typically you get one of these when someone does send you a message. However, it looks like there's something going on with the messaging system (the %%WEBBUG.URL%% looks like an error message).
Go to Home > Messages to see if anything shows up there.
I remember receiving one such message too.
Feeling left out Frankenstein? O_x.
I have never received one of those but have received similar messages you should notify chess.com staff.
They will analyse the message and compare it to their computer database messages and if its a genuine bug problem they will usually look to find a solution, if it is an external third party design attempting to fool chess.com members they will address this too, if its you just trolling you will jepardize your account.
Glad I could help.
I get these messages regularly from other members. I asked one member who sent this to me but he didn´t remember sending this. Sincerely Zimzz99