Invalid object name SQL Server 2008 R2 - Stored procedure

It's SSMS, not SQL Server. If it's an error against the database engine you'll know it (it wouldn't execute the command successfully).

Solution

You need to refresh the Intellisense cache (Ctrl + Shift + R). Or you can go to Edit -> IntelliSense -> Refresh Local Cache.

Intellisense doesn't refresh as quickly as you create new objects. You need to refresh the cache (Ctrl + Shift + R). Or, maybe, don't rely on Intellisense and only worry if the execution fails.

Create a stored procedure by using CREATE PROCEDURE, not ALTER PROCEDURE.