Well, there is obviously a difference in your login form compared to the default login form, no? And, it is something that IE does not like. The best you can really do is look at a page using the default vb code and compare it to a page using your code and see exactly what the difference is in the form and action.

It takes 5 seconds to create a fresh style. Another minute to test if the problem also exists on the new style. Why you don't just follow the suggestions and try it. The result from this test will make it probably clear where the problem is.

Like it is now, you are expecting others to solve your problems but don't want to take any advise or do any testing.