ext3 filesystems - changes ??

[Jeremy Dawson]

I hope this is a suitable forum for this question.

I have RedHat9 installed on one partition.

I have just installed Ubuntu 9.10 on another partition.  When I had a 
choice in the installation procedure, I chose ext3 (since I understood 
that the RedHat partitions are ext3).

Now I can mount the RedHat9 partitions from ubuntu, but trying to mount 
the Ubuntu partitions from RedHat produces an uninformative error message.

Why could this be ? Are there different variants of ext3 ?

Thanks for any help

Jeremy