OssClient.DownloadZippedDocuments Method Giving Error

The OssClient.DownloadZippedDocuments method is throwing the following error sporadically.  The code below that contains this method works the majority of the time.  I would appreciate any suggestions on why this error happens every once and a while. 

Could not download the documents to a zip file. Exception: Object reference not set to an instance of an object.

The code below is throwing the error at the DownloadZippedDocuments method:

//OneSpan connection
OssClient eslClient = new OssClient(C.OSS.API_KEY, C.OSS.API_URL);

//package Id
PackageId pkgId = new PackageId(packageID);

//download zipped documents 
byte[] content = eslClient.DownloadZippedDocuments(pkgId);

//directory path
string zipFileLocation = OneSpan_Listener.Properties.Settings.Default.DocumentsStoragePath + pkgId + "\\";
string zipFile = zipFileLocation + "\\" + pkgId + "_" + DateTime.Now.ToString("yyyy_MM_dd") + ".zip";               

//folder exists check
if (Directory.Exists(zipFileLocation)) 
{
 //delete folder
 Directory.Delete(zipFileLocation, true);
}

//index file check
fullFileName = indFilePath + indFileName + indFileNameExt;
if (File.Exists(fullFileName))
{
 //delete index file
 File.Delete(fullFileName);
}

//zip file download
Directory.CreateDirectory(zipFileLocation);
File.WriteAllBytes(zipFile, content);

//expand zip file                
ZipFile.ExtractToDirectory(zipFile, zipFileLocation);