Waves S1 Stereo Imager error when quitting WL 7

After installing and loading the Waves S1 plugin into the master section, everytime I exit WL 7 I get this dialog:

“A serious error has occurred inside the plugin ‘Waves: S1 Imager Stereo’ Wavelab could control it, but it would be best to save your work and restart Wavelab”

Produces a similar message with Waves H-EQ Stereo.

Is this a WL bug, an incompatibility with Waves, or what?

Windows 7 64bit, WL 7.1 build 543