Well spotted

Actually it was an space, I think the user removed her surname from the username, "silvia surname" became "silvia ", obviously the space was unintended and she's entering her credentials without it and still succeeding to log ... and the user logged has the space ... weird ... Joomla bug I guess ...

Thanks!

Tell her to drop "+" sign from her username and try it that way.

I think she's using IE 8, already told her to do so but I'm afraid she doesn't have a lot of computing knowledge.

Do you keep a record of such errors? I've saved some requests, here's an example:

...blastchat.com/index2.php?option=com_blastchat&task=client&ctask=chat&if=&dt=0&iid=a88f8880c5e2f58f01dc0e50fe5baf67&pk=643e79ff7cd20a26fc1584c9cf741e11&tk=2010-09-01 23:28:47&sc=46a83c5f48955c9622453311fcb7defc&uid=100&ugid=0&nick=silvia+&rid=0&bcid=77&bcv=3.5&avt=&p=Joomla!&r=1.5&d=20

It is very unusual for a single user to have this sort of a problem. And she is single out of few hundred thousands)

All we do right before printing this error message is recreating security code to compare and validate authenticity of the request and data.

What kind of web-browser is she using? Tell her to try with another browser.

She's entering as a logged member and her username doesn't contain any japanese character.

I'm a software engineer and curious by nature so I gave a look at the source code where this security code is generated in the client side (blastchatc.php). Maybe this could help, as far as I understand, in the request uid should have been 100 and username "silvia".

Is he entering chat as a logged in member or guest?
If member, does his username contains japanese characters?

Please, ask him to have latin chars username only and give it a try this way, so we eliminate this possibility of trouble.