I fixed my problems by upgrading from the Ubuntu Linux 2.6.22-11 kernel to the vanilla 2.6.23-rc6 kernel. I hadn't even tried any other 2.6.23 yet. I'm thinking the Ubuntu kernel has a problem due to mismatched or partially backported patches, at least in my case.
Sorry for the misunderstanding.
I fixed my problems by upgrading from the Ubuntu Linux 2.6.22-11 kernel to the vanilla 2.6.23-rc6 kernel. I hadn't even tried any other 2.6.23 yet. I'm thinking the Ubuntu kernel has a problem due to mismatched or partially backported patches, at least in my case.