I know this problem has been brought up a dozen times before, but I have followed the directions in all of the help threads I have found and still have a problem.
I have a pearl 8130, whenever I download and try to install a theme I get the "no additional applications were found for your device" error. I have uninstalled and re-installed the desktop manager with the latest update from the website rather than the cd my phone came with, yet I am still having this problem.
I know this doesn't solve your problem but if you go to the website on your BB where you got the theme from they usually have an OTA link. If you use that you can download the theme directly from your BB.