Does anyone else encounter an error when sending mail from their yahoo.com address to a gmail.com address?

When I receive an e-mail from a gmail.com address, I am unable to reply from my yahoo.com address. Yahoo! Customer Care told me it was probably an issue with my ISP, but I don't believe that. The ONLY time I ever encounter a problem sending mail from my yahool.com account is when I am trying to send to a gmail.com account.
Does anyone else encounter an error when sending mail from their yahoo.com address to a gmail.com address?
I have no problem sending Email from Yahoo mail to Gmail. I have an account at both and as a backup I email important information from Yahoo to Gmail. Although I don't use the reply feature.
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