Server Error in '/' Application

[rosyposy]

I sent an e.card from Hallmark cards and put their address in my favourites, since then when I click on to it the above comes up, with runtime error underneath followed by a full page of instructions which is all gobbley gook to me, should I be concerned, if so, could someone tell me how to get rid of it, but in simple language if possible, please. Thank you.