S/MIME Certificate Location not local?

I recently setup email certificates for both my Yahoo! and Gmail accounts. On my home laptop, encrypting and decrypting emails worked fine. When I imported my certificates onto my USB drive that contained my portable version of Thunderbird, I was unable to decrypt messages. After verifying my Account settings and Certificates were correct I decided to copy the entire ThunderbirdPortable directory to my hard drive at work and everything started working again. I could encrypt/decrypt successfully, but only from the copy on the hard drive.

It seems that there may be settings in the portable app that are not correctly decrypting incoming emails. Does anyone know where in the Thunderbird Portable Config settings I need to check to be sure it is pointing to the correct relative directory to find the email certificates?

As a test, I created a signed, encrypted email using the portable app on the USB drive and mailed it to myself. I can't read it from the portable version of T-bird. But when I copied the portable app directory to the hard drive, I can read the encrypted email. This suggests that composing, signing and encrypting of the outgoing email was successful.

Thanks.