I believe there is an ODBC problem in POCO.
The problem is that POCO doesn’t handle correctly fields for which the column size is not defined. (See the ‘ODBCMetaColumn::getDescription()’ function.) For example: size for fields with type 'nvarchar(MAX)' is not determined. When SQLDescribeCol is called for a field with type 'nvarchar(MAX)', the ColumnSizePtr property is 0 (0 – in that case means that the field size is not determined). When POCO calls SQLDescribeCol to determine the field size based on ColumnSizePtr, it incorrectly assumes that 0 is the actual size of the field.
A workaround would be to change the field type from nvarchar(MAX) to something like nvarchar(1024).