installation error

[wormz]

i just found out recently that i couldn't install or uninstall .sisx files. i'm beginning to wonder what i last installed that made the problem. it always shows "unable to install" or "unable to remove" but has no problem on jar files. i checked the app manager and not all the apps that i installed was there. maybe the registry got messed up

is there anymore solution than reformatting?

thanks:)