Question: I have implemented FB in my application an it is working perfectly in my samsung device o/s 1.5. However in the HTC Evo the FB login dialog disappears soon after loading. it stays for a couple of seconds and vanishes. i have tested it in the emulator 2.2 and it works fine. 

what could be the possible reason of the behavior and how can i overcome it?

just found out that it happens when i am logged into facebook in another application. 
however in applications like photoshop express there is no such issue.

Just what am i missing??

Answer: 
I had the same issue. It was because I was connected with the official Facebook application. I disconnect from the official Facebook application and then I was able to launch the login dialog. The problem is with SSO.

I solved it by forcing the login dialog rather than SSO by passing FORCE\_DIALOG\_AUTH in the authorize methods in Facebook.java.
The issue is actually that you haven't set up your Key Hash for your application with Facebook yet which is required to use SSO. FORCE\_DIALOG\_AUTH actually disables SSO, but this is a poorer user experience. Instead, take a look at an article I put together after struggling with this issue which describes the correct way to tackle your problem:

<http://sean.lyn.ch/2011/07/android-the-facebook-sdk-sso-and-you/>