The XML data type cannot be compared or sorted, except when using the IS NULL operator.

Error:

Msg 305, Level 16, State 1, Line 1
The XML data type cannot be compared or sorted, except when using the IS NULL operator.

Reason for this error message:
1) Comparing XML Data type Columns/Variables.
2) Sorting based on XML Data types

Example Queries:
[sql]
DECLARE @A XML
DECLARE @B XML

SELECT 1 WHERE @A = @B
[/sql]

Fix/Resolution:
1) Check if the query contains direct comparisions based on XML Data type columns/Variables.
1) Check if the query uses xml datatype in the order by clause.
3) Cast the XML Datatypes to varchar(or some other compatable form) and Compare/sort.
2) Use xquery to Compare/sort XML Data types values indirectly.