Help apps wont install

[killerbread]

After I rooted my phone a few days ago when i try and install apps from the market and after it has been downloaded it then says "installation unsuccessful" I have no idea what I have done wrong and have little experience with my htc desire. But I might have played around with some settings with some moving apps to my sd card.

Sorry if I posted in the wrong section and if the question gets asked a lot.

 

[killerbread]

Would resetting my phone to the factory settings make it work? Or would i have to get rid of the root all together?

 

[SUroot]

Clear cache and data on market app first. then maybe on download manager too. if they fail, yes reset

 

[killerbread]

Thanks the reset worked.