Why can’t my Nokia Xpressmusic 5310 download any applications? Everytime I download, it always says invalid.
Daryl, the 5310 can only run java midlets (upto MIDP 2.0). That means, only .jar and .jad applications are supported. The more popular .sis files are not supported. Were you able to download and run apps successfully earlier?
You may want to try downloading apps from different websites (try Mobile9, GetJar, etc.). Be sure to select your phone model on websites before downloading apps. By the way, which website did you use for downloading the 'invalid' apps?
More importantly, try downloading the apps from a computer, and transfer it using Nokia Suite > Phone Browser. If this does not work, you should make a backup of your phone and format it.
1) check compatible apps,ie jad.,jar.,though some phones may also pick sis.apps
2) check your settings especially device encription.If this is on,then your phone is prohibited to instal any app
3) check online certificate check and verification.Any app whose certificate can't be verified by your phone can't be installed.You may turn this off(this would damage your phone)!
or reset your phone and if dont work hard reset but prior make backup of important files.