Error on simple Select statement: Subquery returned more than 1 value
That particular error happens when you are using a subquery in such a way that only one row can be used but more than one row is returned.  For example using a subquery to return a column value.

Since this error only occurs when you have subqueries it is very likely that your tableName is actually a view.  You can easily check this by running the following command.

SELECT OBJECTPROPERTYEX(OBJECT_ID('dbname.schema.tableName'),'BaseType')


If it returns a V then it's a view.  You can then get the text of the view by using the following:

EXEC sp_helptext TableName