getting " Object type cannot be converted to target type." with dataAdapter using storedProc

[Dica]

i'm getting an error when trying set my dataAdapter's selectCommand. the
sqlStatement is a storedProc which takes parameters, so it's constructed as:

sqlSelectCommand1.CommandText = "[uspProjectListUser]";

sqlSelectCommand1.CommandType = System.Data.CommandType.StoredProcedure;

sqlSelectCommand1.Connection = sqlConnection1;

sqlSelectCommand1.Parameters.Add(new
System.Data.SqlClient.SqlParameter("@RETURN_VALUE" ,
System.Data.SqlDbType.Int, 4, System.Data.ParameterDirection.ReturnValue,
false, ((System.Byte)(0)), ((System.Byte)(0)), "",
System.Data.DataRowVersion.Current, null));

sqlSelectCommand1.Parameters.Add("@iCompanyID", SqlDbType.Int).Value = 1;

sqlSelectCommand1.Parameters.Add("@iUserID", SqlDbType.Int).Value = 4;

when i pass this to my dataAdapter as:

oDataAdapter.SelectCommand = sqlSelectCommand1;

i get an error:

" Object type cannot be converted to target type."

i've tried commenting out the parameters, and then have no problems setting
the dataAdapter's selectCommand.

how can i fix this?

tks