Trusted security certificate error

We have recently just switched our main website to be HTTPS only.  We have redirects setup to force all traffic to the secure page.  In our testing before it went live we had no problems at all.  Our cert is issued through Entrust and it is an Extended Validation cert.  We have had a couple of calls from customers in the field that are getting the following error on launching our page.

The security certificate presented by this website was not issued by a trusted certificate authority.

Security certificate problems may indicate an attempt to fool you or intercept any data you send to the server.
We recommend that you close this webpage and do not continue to this website.

We have had her reset advanced settings in the browser, check her time and date, and verified she is typing in the correct web address.  This is only happening to her and a select few, is there anything we can check on her computer that would force our site's cert to be trusted, or is it possible that there is a corruption of some file on her computer.

Any help is greatly appreciated,
Thank you.
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What version of IE is this user on?  Support for extended validation requires IE 7 and above per this:
cbitsupportAuthor Commented:
Sorry I meant to say that in the initial post.  She has IE8.  Also we had her check her intermediate certs and she has nothing listed in IE.  It sounds like a corruption of her base certs on IE.
Yeah I agree it sounds like something local to her.  Not sure what level of access you have to make changes on her machine, but some other things to try would be to download and install a different browser like Chrome or Firefox, and see if you still get cert errors.  You should also be able to obtain a root certificate from your cert provider and try manually installing it on her machine to see if it clears up the trust issue.

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cbitsupportAuthor Commented:
The user did not have any root certs for any providers.  We had her do Windows Updates and an IE patch solved the problem.
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