I installed several themes on my E70 this morning no problems. I installed them on my SD card but decided afterwards to reinstall them on the phone memory. To clean out the SD card I reformatted it via the phone menu. Ever since I did that, it refuses to install anything, saying "unable to install". Even if I install something to the phone memory, it goes thru the whole process as per normal, then when the progress bar reaches the end, it pauses for a few seconds than gives the error message.
It still syncs fine, and the directory structure is fine on both media.