Implicit conversion from data type nvarchar to varbinary(max) is not allowed
===

I get this exception when I try to insert a DBNull.Value into a **nullable** varbinary(max) field:

    Implicit conversion from data type sql_variant to uniqueidentifier is not allowed. Use the CONVERT function to run this query

Thats my code:

      insertCMD.Parameters.AddWithValue("@ErrorScreenshot", SqlDbType.VarBinary).Value = DBNull.Value;

I know there exist duplicate questions on SO, but I do NOT use any String like the others do.

What do I wrong?