do a select * from sys.servers
quite often, the alias for your linked server is different than the name of the actual server.
it's the name of the linkedserver, not the name of the real server, that you need to use to construct the synonym.
so for example, while the actual server might be named [SQLCLUS3\BIZTALK], i could create the Alias for it as BIZ or MyLinkedServer or whatever i felt was a good mnemonic, so that would be the right portion to use for your synonym.
[BIZ].[BizTalkMsgboxDb].[dbo].[Tablename]
[MyLinkedServer].[BizTalkMsgboxDb].[dbo].[Tablename]
Lowell