unable to get auth token in flickr

Question

Hi,

I am trying to access flickr services from android ,

to get the full permissions ,

first of all i fetched forbs using flickr.auth.getFrob method by integrating & converting in MD5

secret + 'api_key' + [api_key] + 'method' + 'flickr.auth.getFrob'

i successfully got the frob , but the problem came when i request a authorized token by integrating & converting in MD5

secret + 'api_key' + [api_key] + 'frob' + [frob] + 'method' + 'flickr.auth.getToken'

but unfortunately i am getting invalid frob , i don't why whats the problem.