I successfully downloaded and installed the Series 60 theme studio onto my pc. (running windows XP)

however, when trying to transfer a theme to my 6630, i save the installation package onto my desktop and run the Nokia Application Installer. this program begins the transfer of the theme to my phone then tells me to finish the installation on the phone UI. thats fine, but when i look at my phone, it displays the following message:

Installation Security Error!
Unable to install!

ehhh..why exactly? can anyone shed some light on this situation for me please?? it's probably something very simple like changing a single security preference on my phone, but it doesnt seem to be mentioned on any user manual i have read.

thanks in advance,