This was a change from 1.1 to 2.0 of .Net. MS considered creating a cookie of 50 years to be a security risk. This is what happened for you in 1.1 when selecting the remember me checkbox. In 2.0 the NEW default is to set it to whatever
your timeout setting is in the Forms tag in your web.config OR the default of 30 minutes. You can fix this by changing your forms tag timeout value to something large.
<forms name=".DASBLOGAUTH" protection="All" timeout="129600" path="/" cookieless="UseCookies" /> for example with set the cookie to last 3 months. If you check remember me in this setup your cookie
will last 3 months.
You can also add sliding expiration to true which will update the cookie to a new 3 month window every time you login...
<forms name=".DASBLOGAUTH" protection="All" timeout="129600" slidingExpiration="true" path="/" cookieless="UseCookies" />
To recreate the behavior of .Net 1.1 you can use Tim's example under the issue tracker "Remember Login doesn't work" or item #2951: