I use reflector to decompile a asp.net dll, after that I find the bug and fixed it, now I want to compile it back to a dll, then I can deploy, but it seems that I can't how can I do this ?
You have two choices, either you use Reflector's addin Filedisassembler, which is free, or commercial ( and pricy) .net dissemblers such as spices.net or salamander decompiler.
I used Filedisassembler; the quality of the decompiled code is very bad. The decompiler code cannot be recompiled.
I'm sure about the quality of commercial decompilers but I suspect that it would be much better.
Edit: To use Filedisassembler, go to Reflector, View->Addins, click Add and select the Filedisassembler.dll.