Could not load file or assembly 'Oracle.DataAccess' or one of its dependencies. An attempt was made to load a program with an incorrect format

I  had deploying an asp.net application to a windows 2008 64bit server. the application uses odp.net to connect to an oracle database. but when I tried to access it I kept getting an error saying:

“Could not load file or assembly 'Oracle.DataAccess' or one of its dependencies. An attempt was made to load a program with an incorrect format”

pulling my hair for sometimes I couldn’t find any logical explanation for this as the dll named ‘Oracle.DataAccess’ was already there in the bin folder. but for some odd reason this was the problem itself. I had to delete the dll from the folder to have the application working.

I don’t have any explanation for this as of now but will update this post as soon as I figure out the cause.