"key expired" from PGP 6

[Joseph Bruni]

I have created a key originally with an expiration date. Subsequently, 
I removed the expiration date on both the primary and sub keys. In GPG 
1.2.1, this is working just fine. However, when I try to import the key 
into PGP 6, PGP is complaining that the key has expired even though in 
GPG the "expires" shows as "never". Can someone explain what is going 
on? I have tried to delete the old key from the PGP system an re-import 
but that does not seem to help.