Steam App comes up with error 1202, how do I fix this?!

[miz]

Whenever I try to use the app to trade, it comes up with "Error Loading Page The Certificate for this server is invalid. You might be connecting to a server that is pretending to be which could steamcommunity . com put your confidential information at risk. -1202"

I have no idea how to fix this, please help.

[Pubert]

try redownloading the app. or signing out of steam and again

[miz]

ok ill try it tnx for a reply