linq to sql error

In a C# 2008 desktop application, I have the following statement that give when an error when the code points to a different database:
eRPTDataContext rptDataaddRVW = new eRPTDataContext();
var eRPTaddRVW = (from a in rptDataaddRVW.eRPT_Transaction_Trackings
                   where a.Package_ID == packageId
                   select a).FirstOrDefault();

Here is the error message I get:
2013-02-04 16:13:15.3731|ERROR|erptsampleclient.eRPTSample|Error Processing --> Specified cast is not valid.
2013-02-04 16:13:15.3731|ERROR|erptsampleclient.eRPTSample|************* Stack Trace *******************
2013-02-04 16:13:15.3887|ERROR|erptsampleclient.eRPTSample|   at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
   at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source)
   at erptsampleclient.eRPTSample.addNewReviewPackage() in C:\_svn\Cas_client\erptsampleclient\eRPTSample.cs:line 1308
2013-02-04 16:13:15.3887|ERROR|erptsampleclient.eRPTSample|Error Processing --> Specified cast is not valid.
2013-02-04 16:13:15.3887|ERROR|erptsampleclient.eRPTSample|************* Stack Trace *******************
2013-02-04 16:13:15.4043|ERROR|erptsampleclient.eRPTSample|   at erptsampleclient.eRPTSample.addNewReviewPackage() in C:\_svn\Cas_client\erptsampleclient\eRPTSample.cs:line 1369
   at erptsampleclient.eRPTSample.Main(String[] args) in C:\_svn\Cas_client\erptsampleclient\eRPTSample.cs:line 154
2013-02-04 16:13:23.3135|INFO|erptsampleclient.eRPTSample|******************ADD (CREATE) REVIEW (RVW) (METHOD 2 CALL)**********************
2013-02-04 16:13:28.8359|INFO|erptsample.ERPTProxy|The number of attachments in the list are ->1
2013-02-04 16:13:54.2171|INFO|erptsample.ERPTProxy|add review package successfully for rvw pkg id: RVW0204201300524 return code = 0
2013-02-04 16:13:58.5227|INFO|erptsampleclient.eRPTSample|Review Package was created successfully for Package id: RVW0204201300524
2013-02-04 16:13:58.5695|ERROR|erptsampleclient.eRPTSample|Error Processing --> Specified cast is not valid.
2013-02-04 16:13:58.5695|ERROR|erptsampleclient.eRPTSample|************* Stack Trace *******************
2013-02-04 16:13:58.5851|ERROR|erptsampleclient.eRPTSample|   at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
   at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source)
                                                      
When I change the code to the following:
var eRPTaddRVW = (from a in rptDataaddRVW.eRPT_Transaction_Trackings
                   where a.Package_ID == packageId
                   select new { erptPackageID = a.Package_ID, erptFileLocation = a.File_Location }).FirstOrDefault();

I do not get an error.
The problem is I want to be able to update the database row I just accessed and the linq will not compile clean to let me do that.

I am getting the follwowing error message when I try to access a specific field:
Error10'object' does not contain a definition for 'erptFileLocation' and no extension method 'erptFileLocation' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)C:\_svn\Cas_client\erptsampleclient\eRPTSample.cs132056ERPTsampleclient
Here is the code I am trying to add:
    if (eRPTaddRVW != null)
       {
         eRPTaddRVW.erptFileLocation = RVWFile; // save location of original spreadshgeet
         rptDataaddRVW.SubmitChanges();
}

Can you tell me what I can do to solve my problem?