@Tinus72 My guess is that these plugins are simply not compatible because Acid is too old.
You'll likely need a plug-in chainer like Plogue Bidule or DDMF Metaplugin as a workaround. You first load the plugin chainer as a VST and then load the Waves plugin inside the chainer.
Waves 16 plug-ins open in Acid Pro 11 for me, along with all other plug-ins I have installed.
I have updated the four / six audio_plugin_*_server* files, so this maybe the solution, as suggested in another post (@SP may remember the link).
I originally tried the files from Vegas 22 and SF Pro 18, but both crashed Acid for me on start. So I think I used the files from Music Maker 2025 (trial) in the end. These worked after a force rebuild plugins.
Vegas, SF Pro, most SF Audio Studio, ACID and Music Maker seem to use the SF VST interface so some recent versions of these should work (whereas SF Audio Studio 12.6 and SF ACL4 appear to use the Samplitude VST interface).