If the client has the Amazon Album cover enabled and do not have the Amazon Aff ID entered, when they upload mp3s in the web based file manager they get a JSON error,

In my Centova v3 ADMIn settings I do not have my default Amazon ID entered however I also have

Allow client-specified Amazon® affiliate IDs:    set to NO (default)

 

How exactly are you determining that the JSON error is being caused by a missing Amazon ID?  Could you give me more info about the JSON error?

I tried exactly what you described:

Client Settings

Albums -> Settings -> Amazon at the top of the list
Albums -> Amazon.com -> Amazon affiliate ID = blank

Admin Settings

Albums -> Amazon.com -> Default Amazon affiliate ID = blank
Albums -> Amazon.com -> Allow client-specified Amazon affiliate IDs = No

Had no problems uploading MP3s.  And that's how it should be... Amazon honestly doesn't care what you enter for the affiliate ID -- if it's a bogus or mistyped ID, they still allow the link, they just don't credit anyone for any sales it generates.   In testing I use something like 'blahblah123' and it works just fine, and blank should work just as well.

Ever since I added my Amazon ID and web services key in my Centova ADMIN settings I cannot reproduce either, even tried removing my default ID but still worked fine,  but here was the error (pulled that from my live chat)

Bad JSON response: Invalid JSON:
Fatal error: Call to a member function get_node_by_name() on a non-object in /usr/local/centovacast/system/albumds/class_AlbumDataSource_lastfm.php on line 99

This has happened a couple times but I had remembered I got that error last year and figured out the solution then, one of my testers/friends had the problem come up the other day, he was just click happy enabling and clicking on everything he could but as soon as I disabled Amazon albums he was again able to upload.

Ahh, that's a last.fm error (note the ...AlbumDataSource_lastfm.php in the message).

Basically what it means is that CC submitted a request to last.fm, but last.fm's response did not contain a <lfm> XML element.  The <lfm> element is the outermost element of ALL responses from last.fm's API (even error messages) so the fact that it didn't exist basically means that the connection somehow failed.  Most likely a temporary connectivity problem between you and last.fm's servers, or a brief outage of their API service.

I'll change it so that it's handled more gracefully though -- it certainly shouldn't cause a JSON error.