Is there a possible that unity 4 will automatically fix all the problems of the script ??
Purchasing Unity 4 Pro does not fix any errors you may have in a script. The syntax for the code is no different between Unity Free and Unity Pro. You may want to look at the license comparison page to see the benefits of Unity 4 Pro but it will NOT fix any errors in your script. If you have some errors in your code that you are having trouble with feel free to post them here in a detailed question and we will do our best to help you. We won’t write the script for you but can help with a couple errors you may have. Cheers!
If you mean fix compilation errors: No.
If you mean fix logic errors: No.
If you mean fix issue relating upgrading from 3.5 to 4: No.
Here’s a guide for upgrading your 3.5 code for 4.
If those don’t cover what you expect to be fixed do you have an example of what you think it could possibly fix?