added my hotmail account back on my iphone. I am constantly prompted for my password everytime I try to read my mail. It never did this previously. Any suggestions?

I recently setup my Hotmail account on my iphone4 again. It constantly prompts me for my password. It will then work for a while then keep prompting me for my password. It was so annoying I had to delete the account. Does anybody know what is causing this and how I can prevent it from happening? When I had this account installed previously it worked fine without this annoying prompting both on iphone 4 and iphone5. Thanks.