Cannot access Webmail using IE9

[#1]

I have just acquired a laptop with windows7 and IE 9.I cannot access my webmail when using IE9.  I am repeatedly told that I have entered a wrong username or password.
I can access webmail from my old pc running on windows XP, and bizarrely, I have now installed Mozilla Firefox on my laptop and was instantly able to access my webmail.
Has anyone any clues why?  Plusnet say as it is a software problem they cannot help (didn't even say - "wehave/have not heard of that one" .
Is it a setting?  If so where?  I have set plusnet as an allowed website, including https:// .
Any  help appreciated.

[#2]

No problem for me using Windows 7 Home Premium with Service Pack 1 64-bit version and IE9.  IE9 threw up a prompt to remember my password at the bottom of the Window - I said no. 
I don't have Plusnet set as an allowed web site (and if that ever works it's only by masking some other problem). 

[#3]

If there was a general problem accessing webmail using Win 7 and IE9 we'd have seen many, many postings about it before now. It's 99.9% certain that it is something at your end.

[#4]

I'm not sure that many people use the Plusnet webmail interface, which seems to me to be stuck somewhere in the mid 1990s.  But I agree it has to be something specific to fish2011's computer.  Could you have made a typo then asked IE9 to remember the wrong password?

[#5]

Are you able to view/delete the remember entry for user/password in IE's list?

[#6]

You can just overtype the automatically inserted 'blobs' to update a remembered password, it then asks if you want to replace the previously remembered one (I think).