lets double check some settings...by abstracting out your code to be anonymous (SERVERA and SERVERB, something got lost, i think.
first, i don't think its necessary to use EXECUTE AT.
you can use an alias just like you were using.
the syntax you are using for update requires the SERVERB to be a SQL server...
the command you are using requires SERVERB to have a linked server to SERVERA
from what you posted, the opposite is true..SERVERA has a linked server, but not necessarily the reverse.
Lowell