c# - Mismatch columns in the primary key : versus

Question

While merging two DataSets in C# .net framework 4.0, it raised an error:

Mismatch columns in the primary key: <target> versus <source>

My 1st Dataset is from SQL Server of datatype Varchar, while other is from Oracle database of datatype Varchar2.

// SQL Server database
OrgStockMaster.PrimaryKey = new DataColumn[] { OrgStockMaster.Columns["PkID001"] };

// Oracle database 
dtOracleStock.PrimaryKey = new DataColumn[] { dtOracleStock.Columns["PkID001"] };  

While doing this,

dsStockMaster.Merge(StkFrmOracle);
DataSet dsDiff = dsStockMaster.GetChanges();

It raises this DataException :

Mismatch columns in the primary key: <target>.PkID001 versus <source>.PKID001.