Whenever this happens to me, I press Ctrl+Shift+R which refreshes intellisense, close the query window (save if necessary), then start a new session which usually works quite well.
This error may ALSO occur in encapsulated SQL statements e.g.
DECLARE @tableName nvarchar(20) SET @tableName = 'GROC'
DECLARE @updtStmt nvarchar(4000)
SET @updtStmt = 'Update tbProductMaster_' +@tableName +' SET department_str = ' + @tableName exec sp_executesql @updtStmt
Only to discover that there are missing quotations to encapsulate the parameter "@tableName" further like the following:
SET @updtStmt = 'Update tbProductMaster_' +@tableName +' SET department_str = ''' + @tableName + ''' '