I have deployed my system developed on 32 bit to 64 bit production environment and was continuously getting bad image exception.
After a lot of drill down I found that the issue was due to deployment of custom web parts developed for share point site.
The issue was that I was referencing sharepoint 32 bit dll from my visual studios for accessing moss object model. Issue get resolved after replacing dll at production environment from (\Program Files\Common Files\Microsoft Shared\web server extensions\12\ISAPI).
Though the problem is resolved but as I have compiled custom web part with 32bit dll I still thing compilation with 64bit will be better option this will lead to an issue that development for 64 bit require 64bit machine.