Default Property for .Fields and PropertyBag problem

[VB400]

I'm having a problem with the following code:

objPB.WriteProperty "UserName", .Fields("UserName&quot

This gives me the following error message:

Run-time Error 330. Illegal parameter. Can't write object because it does not support persistence.

When I add the .Value property as in the following line, it works just fine:

objPB.WriteProperty "UserName", .Fields("UserName&quot.Value

I know that .Value is the default property and should be picked up automatically. As a matter of fact, I use the .Fields without the .Value everywhere else and it works just fine. For some reason, it just doesn't work with propertybags.

Any ideas? Tarek