>I have read somewhere that the disabled attribute is not supported in IE, prior version 8. That would explain. However, to test that, I would need to install IE 7 somewhere. I will add more input to this once I can simulate it.

I think that only applied to 'option' controls - not 'input'

However, I thought that if you disabled before submitting then the submit doesn't happen. i.e. your code should be:

loButton.Attributes.Add("onClick", "document.Form1.submit(); this.disabled=true; return false;");