Check the exception for a call stack, it should help narrow down which part of the export is failing.

Also, try retrieving the document image/text data using a different method and see if that also fails with Access Denied:

PageInfo page = lfpages.GetPage(1);

String imageTempFile = Path.GetTempFileName();
using (Stream imageStream = page.ReadPagePart(PagePart.Image))
using (var tempStream = File.OpenWrite(imageTempFile))
{
    imageStream.CopyTo(tempStream);
}

String textTempFile = Path.GetTempFileName();
using (Stream textStream = page.ReadPagePart(PagePart.Text))
using (var tempStream = File.OpenWrite(textTempFile))
{
    textStream.CopyTo(tempStream);
}

Thanks for the tip.

I tried to implement your suggestion and my code failed when attempting to get any page info, same error.

DocumentInfo documentInfo = Document.GetDocumentInfo(entryIdIn, sessionIn);

PageInfo page = documentInfo.GetPageInfo(1);//Fails here with the 9013 'Laserfiche.RepositoryAccess.AccessDeniedException'

For some reason that account lacks read access on the document.  Try calling documentInfo.GetEffectiveRights() and verify that the user has EntryRights.Read.