I love Visual Studio 2008. I even refer it to clients when setting up the SalesLogix Web Client to have available in case there is any debugging that needs to be done.
More information can be located from here
The fix is to locate the action attribute in the Login.master page on the form tag and remove the action attribute from the tag completely.
Note that this is a SLX Web Client 7.2.2 and below issue and has been addressed for the 7.5 release
Further testing reveled that base.master, default.master, login.master, and dialog.master all had the action attribute set. To fully fix this issue the attribute needs to be removed from all of these pages. For example if you do not remove the attribute from base.master navigation will be broken on the detail pages such as account.ascx
Cheers, and have a good night