I also have a Dell Axim X51v with this error. By sheer luck, i found a workaround for it.
There is a tool collection, called SKTools (
www.s-k-tool.com). One of them is for deleting the notification queue and since the error message says something about notification i tried it.
It worked! The error disappeared. And whenever i get the notification error again, i simply use this utility to get rid of it.
I'm not the WM5 specialist, but it seems, that the odyssey clients makes a wakeup entry in the notification queue every time it starts. The bad news is, that it looks like the notification queue can only handle a certain number of entries (don't ask me how many). So, when the queue is full, the odyssey client tries to make his entry for about one minute, before he produces the error message and i think that causes the delay.
I know, it is not really a solution, but at least for me it helped and i hope it does also for other people, owning the absolutely facinating Dell Axim X51v.
Greetings to all of them
quirken