Nokia :: Problem Importing Some DER Certificates On E72

I would like to make a connection to a certain IMAP server that requires TLS/SSL. I did setup the connection in the EMAIL application that comes with my Nokia E72, but even though I never received an error, it did not work. (Connecting to other mail servers, IMAP and POP, with and without SSL works just fine using EMAIL, so I guess I know what I am doing...)

Using Profimail on the E72, I discovered that there is actually a Symbian generated error when trying to establish the connection, the error code is "-5". Reading about this, I discovered that I need to import a DER style certificate for the mail server. So I exported the certificate for that server in the correct type from my Thunderbird installation on the desktop and tried to import it using the file manager on the E72. However, the file manager comes up with "Unable to open. File type not supported" The strange part is, I went ahead and exported the DER style certificate for the SAME mail server from last year, which is now expired... and it imports just fine. (however, it is useless, as the certificate expired)

I know this is a rather complex scenario! I am trying to describe all the relevant steps here but I am happy to provide even more details.
So I am wondering.... how comes the file manager will import some DER certificates just fine, and others not? I attached both certificates to that posting, the "rijndael_current.der" is the one that does not import, the "rijndael_expired.der" imports just fine. Both certificates look the same to me, and they look the same to my Thunderbird mail client on the desktop. (just found out I can only attache jpegs... great... :-( )