Since loading SP3 I have had some issues with labels disappearing. I know the cause of the error but not the cure.
Say my label expression is:
[Name] & vbnewline & [ID]
Somewhere in my work the label expression changes on its own to:
[sde.sde.Stores.Name] & vbnewline & [sde.sde.Stores.ID]
Then at some point the labels start to fail so I have to manually erase the [sde.sde.] prefix to fix them.
I routinely turn on and off definition queries and use joins so I'm sure the cause is one of those but this only started in Arc10 SP3.
I'm thinking maybe the reverse solution to my problem might help. Add in the layer name to the label expressions.