It's so good when "one of those things" causing head-scratching, is overcome Well done MM.

This is usually the part where someone says do a complete uninstall, 'turn it off, then turn it back on again' - the do a fresh re-install of the latest Pianoteq.

So many moving parts possibly - but before doing the above ..

Question:

Did you make the fxp while using Pianoteq as a plugin?

(I haven't experience an error from doing that - just it may be possible the host added some "lines" or text/something to the true FXP).

SO maybe the first thing I'd do (knowing that extra info), is open the FXP in a text editor.. see if there's something obvious like "Sibelius versioning" or whatever else which isn't included in a normal FXP created in Piantoeq standalone.

Maybe use a file 'diff' app for that task.

Hoping it's "at worst" something you can re-make.

Like, at 'next worst' - open Pianoteq as plugin - and open another standalone instance.. A/B to view your desired FXP in the plugin version, and step through each control, copying the settings to the standalone Pianoteq. Then try "Save as" in standalone, save to desktop of somewhere and try loading that into your Sebelius session.

Hope something like the above might help. Let us know how you go.

Heya MadMusicologist,

Wonder if copying a dll to a Sibelius folder might cause the issue.

Apparently not: At Sibelius they also told me not to add any plugin dll-files to the AVID VSt-folder. So I removed them and pasted them to the VSt-folder of my DAW Cakewalk (by Bandlab), there it is required, so the DAW would find them easily. After that, I launched Sibelius and changed the playback engine options and set the new path. After relaunching Sibelius it found all the plugins - aha, that worked - however, when I tried to load the fxp-file to pianoteq, Sibelius crashed again.

As I pointed out above.

Indeed, that's possible, and I had selected per default that VSt-folder at Cakewalk.

Thanks so far, but I have the feeling something must be screwed up with my fxp file suddenly.
By the way, when I open the pianoteq standalone, and click "load a fxp-file", I never get anywhere: Pianoteq always returns "not an fxp-file". However, when I use Pianoteq as plugin, the same file works fine. So I am really in a bad situation since I cannot continue my project properly.

Wonder if copying a dll to a Sibelius folder might cause the issue.

After installing Pianoteq, I've never needed to 'copy a dll' somewhere. Install is all.

(*you may have reasons - but it does seem the likely issue, based on the info provided).

I point to it, because I use various DAWS and hosts/OSs and over time, I've never had to do anything beyond installing Pianoteq, to have it run actually very close to 100% error free everywhere (as standalone, or as a plugin in any DAW or host).

Instead of manually copying any 'dll' to a special custom locale, is it alternatively possible within Sibelius settings to create a path to where all VST's install to? (like the Steinberg and/or other common directories?).

Or, whilst installing, is it possible to tell Pianoteq to install the plugin path as the custom one you want?

[For the many times I've updated Pianoteq, I actually cannot just now remember what path information it asks for when installing - because, I have never had to jink things in custom ways.. I've pressed "yes" during installs.. this is how I prefer, and with audio applications, to try to make all programs use "well worn paths" - honestly, this does seem to have improved in the last half dozen years to a decade. I now feel there are, at least for me (with a great many audio tools), less and less valid reasons to customize disperate folders for multiple, potentially clashing installed audio 'extensions'.]

I get very nervous, when a plugin warns me "Be sure to select the correct path" on install.

Keeping things as standard as possible, rather than a jungle of custom paths (for reasons) has turned out the winning way, at least for me.

Hope that gets it, but let us know - and good luck with that music.