Most likely that's a problem with your browser's settings. Specifically if you have your browser set to delete cookies automatically or have add-ons or security software that performs that function for you. I state this because Messenger connects to your browser and needs those login cookies to preform the switch between the client and your browser.
Here are the steps to check if your browser is clearing cookies automatically:
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Verified answer
Hi Jeff,
Most likely that's a problem with your browser's settings. Specifically if you have your browser set to delete cookies automatically or have add-ons or security software that performs that function for you. I state this because Messenger connects to your browser and needs those login cookies to preform the switch between the client and your browser.
Here are the steps to check if your browser is clearing cookies automatically:
http://help.yahoo.com/kb/index?page=content&id=SLN...
If you've confirmed that is not happening, and you still experience this issue, please try the following steps to reconfigure your web browser:
http://help.yahoo.com/kb/index?locale=en_US&y=PROD...
Hope that helps!