Can you give some more information about version number and what kind of errors do you have exactly, which dll's and where do you see the errors?
What do you main with "I pasted web.config"?
Does it help when you use the original web.config file? which is distributed with the Sitecore version you use.
Also the "new sitecore application" is that a custom part on top of Sitecore?, does it overwrites existing sitecore dlls?