Can you verify that upload location you have provided while creating Virtual directory is having files uploaded?
IF you have not created virtual directory crate it.
If virtual directory is created successfully then go to PKS Podcast list, go to Settings>List settings, Under columns section check if you find "NFS Xml Blob" entry.
then follow below steps
Go back to the settings for the PKS Podcasts list, click Podcast Files in the Columns section.
Delete the column.
Create new Column named as PodcastFiles of Type Network File Store.
Rename this column to Podcast Files.
and once again create virtual directory as given above.
Do an iisreset.
and now again upload and verify.