Sony Ericsson :: K800i - Apps Or Games - Operation Failed
Check the file format of the application if it's compatible or not.
try to download here : http://phone.mobile9.com/i/sony+ericsson+k800/
If you still got error on installing the applications,try to reset the phone. Go to settings > Master reset and choose if you want to reset only the settings or the entire phone,if ask for a code,the default will be 0000,but if you change the code before,enter your desire code and after that the phone will restart and it will go back to its original settings.