certificate error on Nokia N81

I get certificate error, or unable to install or installation of ..sis file not supported etc. I am not able to install game. Can someone help me ?

thanks

Are the private key and certificate in your CarbideUI still valid? Perhaps they have expired and you have to create new ones.

Nokia N81 supports .sis file
for fixing the certificate expired problem follow these Steps :

Go to: Menu > Tools > App.Mgr > Options > Settings

Software installation: All
Online certificate check: Off