Do you have the details on which CD/discId caused this; i.e the query it made to the web service?

Simon can reproduce this on his computer with any CD. I don't know how to get the query it made to the webservice though.

I don't have a CD drive so I'm not sure how I can help with this. If some could provide a tcpdump of soundjuicer or something, I can have a look

Here you are.
I see the same problem. I have done the standard updates in my system, but I do not remember that I would have updated anything about Sound Juicer.
I tested with CD's that I can find in MusicBrainz. All of them failed. If I try to enter data to Musicbrainz, it suggests directly right CD, but I do not get any feedback to Sound Juicer.

File is created with tcpdump -vv

...and it seems that also Rhythmbox has stopped showing CD titles. I assume that it has same routines as Sound Juicer.
If needed, I can also test it otherwise.

Dunno if this is helpful or not, but . . .the last time I absolutely know for certain that MusicBrainz queries from sound-juicer and/or rhythmbox worked perfectly was May 15th. Queries from both failed for me yesterday (and since). I have not done any software upgrades on this machine of any kind at all since May 1st, well before the last successful query. That fact, plus the fact that most (all?) users are also running into these problems, strongly suggests to me that it's a server-side issue and not an application-side one.

Further info:

Ubuntu bugs reporting that Musicbrainz queries are failing . . .

on banshee:
https://bugs.launchpad.net/ubuntu/+source/banshee/+bug/778090

on sound-juicer:
https://bugs.launchpad.net/ubuntu/+source/sound-juicer/+bug/788921

on rhythmbox:
https://bugs.launchpad.net/ubuntu/+source/rhythmbox/+bug/787475

. . .leaving Ubuntu users unable to rip except by entering disc/track info manually.

A question: did Musicbrainz recently drop support (i.e. within the last few weeks) for RDF queries? If so, perhaps that's the source of the problem – cf. this Ubuntu bug filed against sound-juicer, which was first reported a year and a half ago but apparently still applies:

https://bugs.launchpad.net/ubuntu/+source/sound-juicer/+bug/455461

Thanks for that Chris. Yes, the RDF service has been deprecated for years now, and we have now finally removed it entirely. I see SoundJuicer does use the old RDF MB, but also looks like it uses libmusicbrainz3, which iirc uses /ws/1

I think it depends on the version. For that matter, the same is true for banshee and rhythmbox – older versions use libmusicbrainz4, which did RDF queries. My machine is still running Ubuntu Karmic, which passed out of support just last week. So maybe the reason why some banshee/rhythmbox/sound-juicer users are complaining, but not a flood of them, is because it's just hitting the ones using older versions of those packages?

FYI Banshee issue has a different origin:

Banshee doesn't use libmusicbrainz3, it uses Musicbrainz_Sharp (http://wiki.musicbrainz.org/Musicbrainz_Sharp) which uses /ws/1.
Banshee issue (MBS-2185) comes from its inability to handle CD TOC attached to multiple releases - upstream ticket: https://bugzilla.gnome.org/show_bug.cgi?id=587264.

Ah, thanks for pointing me to that one murdos, I hadn't seen that! I was aware they used /ws/1/, but not that they had this bug, so I guess that's out of our control to fix.

This is a packaging problem. I have spoken with the contributor who added libmusicbrainz3 support to both Rhythmbox and Sound Juicer, and he can confirm they both work if built with the correct bindings. It's a packaging problem by the sound of things, so the Ubuntu/etc team need to rebuild packages.

In Ubuntu this affects Lucid and earlier. Since Lucid is a LTS release I really hope it will get updated.

Until this gets officially fixed you can use the updated package from my PPA at https://code.launchpad.net/~phw/+archive/musicbrainz/ , see my notes on https://bugs.launchpad.net/ubuntu/+source/sound-juicer/+bug/455461

Thanks Philipp, works nice on Sound Juicer for Ubuntu Lucid.