Audio, new instrument tracks play, old instruments not

I am working on a Mac running 7.5.20 in case it matters. I was running 7.5.30 but had lots of problems and rolled back. Today I returned to a project I hadn’t worked on in a while. When I was working on it last, I was just working from audio tracks and had all the instrument tracks muted. After I unmuted them, they would not play. Audio tracks would and new instrument tracks would play as well. I checked to see that the routing was correct but then tried connecting instrument tracks directly to Stereo Out but to no avail. I tried duplicating tracks but the new ones did not play, either. I tried exporting tracks and importing them back in but they still would not play. The best I have been able to come with is saving a track (sans parts) via a track preset. If I go to Media Bay and create a new track by clicking on the preset I created then the new track that appears does play. I guess things could be worse as I can move the parts from the old track to the new and I am right back where I started but there are a lot of tracks in this file and it would be very time consuming and error prone to recreate every track that way. Also, one of the presets I created crashes Cubase when I click on it. Anybody got any ideas?

[Edit]

I forgot to mention that when the tracks aren’t playing the MIDI activity meter for the track is not showing activity

[Edit]

The cause of this and other flaky problems I have been having seems to be ReValver. I had III.V and I began to suspect that was the cause so I upgraded to 4 but it seems to be worse in that the problems occur more often. I was able to identify a problem instance from the VST Performance Meter. I saved a preset, quit Cubase, started a new project, and loaded in the preset and the problem persisted. This seems to exonerate Cubase…this time.