Import Beginning Balances with Dimensions

Hello,

My company is in the process of implementing NAV 2013 and I'm tasked with importing our opening balances. I had done this before in NAV 2009, but apparently the Dimensions are drastically different now and I'm running into a few glitches.

I'm developing an XMLPort that imports a text file containing the basic G/L Acct, debit, credit and a couple dimension values. My understanding of the new dimension set entry is limited, but I was under the impression that I would need to:

1. Insert the Journal line
2. Make sure the Dimension code/value exists (insert if not)
3. Insert a dimension set entry record with the Dim set id from the Journal Line table for each dimension

Here's a sample of how I'm currently attempting this:
Insert Journal line:

GenJournLine.TRANSFERFIELDS("Gen. Journal Line");

GenJournLine."Line No." := LineNo;
GenJournLine."Journal Template Name" := TemplateName;
GenJournLine."Journal Batch Name" := BatchName;
GenJournLine.VALIDATE("Account Type","Gen. Journal Line"."Account Type"::"G/L Account");

GenJournLine.INSERT(TRUE);

If dimension value does not exist, create it (this is done for each dimension I want to attach to the journal line).

IF NOT DimValue.GET('CUSTS',CustDim) THEN BEGIN
DimValue.INIT;
DimValue.VALIDATE("Dimension Code",'CUSTS');
DimValue.VALIDATE(Code,CustDim);
DimValue.INSERT(TRUE);
END;

Now insert the dimension set entry

JnlLineDimension.VALIDATE("Dimension Code",'CUSTS');
JnlLineDimension.VALIDATE("Dimension Value Code",CustDim);
JnlLineDimension.VALIDATE("Dimension Value ID",DimValue."Dimension Value ID");
JnlLineDimension."Dimension Set ID" :=  GenJournLine."Dimension Set ID";
JnlLineDimension.INSERT(TRUE);

When I run this I get an error that I don't have "insert" permissions on the Dimension Set Entry table.

I must be doing it wrong, but I cannot find any resources that help point me in the right direction. Any help would be appreciated.