For those of you that haven’t read about this at Techmundo or at E-Series read on:
If you get a certificate error when attempting to install 3rd party software on your S60 3rd Edition smartphone (Nokia E61/E61 or other), it means that you haven’t enabled installation of unsigned SIS files. Go to Tools> App. Manager, choose Options> Settings and set Software installation to All and Online certif. check to Off.

Remember that this is like removing one lock from a door.
But I think that this can’t really harm you because you choose what you download.
