ZFS: Can't find pool by guid

[Willem Jan Withagen]

Hi,

I upgraded a server from 10.4 to 11.1 and now al of a sudden the server 
complains about:
	ZFS: Can't find pool by guid
And I end up in the boot prompt:

lsdev gives disk0 withe on p1 the partion that the zroot is/was.

This is an active server, so redoing install and stuf is nog going to be 
real workable....

So how do I get this to boot?

Thanx,
--WjW