SSMS Cache

The Microsoft SQL Server Management Studio is the Visual Studio for DB guys, with SQL Server 2008 R2, the IntelliSense feature in SSMS is awesome.  It saves time and the experience is cool.  Some time the IntelliSense will not work.  There can be several reason for this. 

• You may be typing multiple statements with out proper batch separation (GO). 
• The underlying schema is changed.

If it is schema change you can try refreshing the Cache, must of the time it helps.