IK Multimedia VST plugins Sample Tank and Syntronik are opening, but not working in Cubase 15, i.e. It is not possible to load any of their included instruments and have them to sounds.
In Cubase 14 both Sample Tank and Syntronik are working as expected.
I donāt think Iāve tried Syntronik in Cubase 15 (itās not a plugin Iāve used much, if at all, despite its having been included with the version of TotalStudio MAX I have), but Iām definitely using SampleTank 4 instruments in my current Cubase project (Cubase Pro 15.0.10). I am using the VST3 version of the plugin. (I havenāt used VST2 plugins since Cubase 14 disabled them by default.)
If the plugin is loading but not showing instruments, you might check that the path t the sounds is set right in the SampleTank/Syntronik settings. However, Iād think it would be if itās working in Cubase 14 as Iād expect the setting to be specific to the plugins, not the version of the DAW.
It is the VST3 versions of Sample Tank 4 and Syntronik 2 I am using. Both Sample Tank 4 and Syntronik 2 are working as expected in Cubase 14 and earlier Cubase versions and also as stand alone applications. It is only when I open them in Cubase 15, version 15.0.10, the selection of instruments is not possible. I have also noted in the settings window, when hitting the Rescan button for Sound Content. The scan will never start. I think there is a problem in Cubase 15.
You donāt mention if you are on Windows or Mac. I wonder if itās possible that may make a difference. FWIW, my notes above are for Windows 11 25H2 fully updated. SampleTank 4 MAX version is 4.2.6, and, as mentioned above, Cubase Pro version is 15.0.10 ā basically everything is fully updated. I donāt use SampleTank all that often, but I am using it on my latest project due to some specific instruments I needed (from memory, I think harmonica and accordion) that are either non-existent or just not very good in my Kontakt libraries. These were all loaded first in 15.0.10, too, as I just set up the project this past Thursday.
I will say that I did notice the building the library database took a while as I hadnāt used SampleTank in a while prior to Thursday (and the MAX package includes a ton of libraries). I also have a recurring āuser errorā scenario most every time I use SampleTank, due to such long periods between uses, where I forgot where to actually load the sounds and ending up clicking around the interface a bunch before figuring it out. 
For troubleshooting purposes, since you have it working in Cubase 14, what happens if you backup the Cubase 14 project where it is working, then load the backup version of the project in Cubase 15? Does it load the instrument in that case?
The other thought that comes to mind is if there is some permissions-related issue with your Cubase 15 installation. Again, just for troubleshooting purposes (decidedly not something you want to do for regular use), assuming youāre using Windows, you might try using the Run as Administrator capability when starting Cubase 15 to see if that makes a difference. If it does, then there is likely a problem with your Cubase 15 installation. Someone else may be more knowledgeable on specific steps to take to resolve that, but my best guess would be to totally uninstall Cubase 15 (not necessarily its libraries and other add-ons), then reinstall it, making sure that, when you install it, you are using an account with Administrator privileges and respond affirmatively to the system prompts that ask about elevating privileges for the installation. (Since SampleTank is working okay as standalone and in Cubase 14, I donāt think there is any need to also reinstall SampleTank.)
The only other thing I can think of is, if you do enable VST2 plugins in Cubase 15, is it possible you are accidentally running the VST2 version rather than the VST3 version? (If you donāt enable them, it wouldnāt be possible.) An easy way to be sure would be to go into Plugin Manager, look for SampleTank, and, if there is a VST2 version that shows up, hide it from the menus (something I always did with VST2 versions of plugins when I had VST3 versions prior to Cubaseās not supporting VST2 plugins by default). Then create a new instrument track with SampleTank now that the VST2 version canāt be in your menus to see if there is any difference. (That said, even if you were accidentally loading a VST2 version, Iād be surprised if the VST2 versions would behave differently from the VST3 version in this area.)
Perhaps it is also relevant that I am loading SampleTank only as instrument tracks, not as rack instruments. (I remember there was an issue with Omnivocal if using it as a rack instrument rather than in an instrument track.)
Last thought, at least for now, is there is another thread on these forums regarding trouble with loading SampleTank on Cubase 14. Independent of the Cubase version number, it sounds like it would be a different issue from what you are reporting. However, it might be worth reading through, just in caseā¦
Same for me on Mac, initial library scan after a couple of months takes a while, but then ST4 works.
And Syntronik 2 works too.
Oh, one other thought: After you experience this issue, if you are on Windows, it may be worth going into Event Viewer to see if there are any relevant event entries as those might possibly provide some clues. Iād expect the most likely location would be the application log, but a secondary possibility might be the security log. Especially for looking at the security log, which tends to get loads of entries, it would be especially helpful to note the specific timestamp on your system clock when you experience the issue to narrow things down to a smaller set of potentially related entries.
Thank you Paul for your great support. I found the problem om my Mac because of you.
The Full Disk Access in Privacy and Security setting for Cubase 15 was for some reason not set, even though I had reinstalled Cubase 15 one time before. Now everything works as expected for both Sample Tank and Syntronik.
Glad you solved your problem. nuendo 14 moved opus to a āsamplerā library and now the songs that use opus refer to the wrong directory.