I have the same problem. Bought the 2017 samplitude and recently the pro x4 upgrade. All track fx I have installed in the 2017 won't work any more with pro X4. Why the hell did I bought and expensive upgrade!!!!!!!!!! All my unfinished music projects, I assumed I could finish in X4, must be finalized in version 2017. Cause the vst-effects have an other image/build. Same goes for other track effects. You can load older VIP projects in a higher version, but all vst-i and tracks fx won't apply. You must reset all those parameters, which is in my case too much work.
SO, if you want to use your old music project files without resetting all parameters, DON'T buy an upgrade to pro X4 or X3.....
Are you sure about getting the Electric Bass VSTi with Samplitude Pro X2? I have Pro X2 and it's not there, but Bass Machine came with it.
Did you keep the installation files for X2 (I keep them all)? If so, then you can see which instruments were included. If not, then you may want to reinstall X2 along with its instruments as they may have been removed when X2 was uninstalled. Then they should show up in X4.
I presume that you downloaded and installed all of the additional content under Help, Download Instruments and sounds.
Pro X4 is a 64bit program as was Pro X3. I don't recall if Pro X2 was a 32 or 64 bit version or both. You may want to check. If you have old projects with 32bit VST's, make sure to add the 32bit VST path or Pro X4 won't find the plugins.
There is a dedicated Samplitude Pro forum here that you may want to join.
Thanks to all those members that took the time to respond, Kraznet the Almighty solved this issue for me, I downloaded what I needed from his link in the SAM forum and bingo all is well. but... it's sooo unreliable...crashing with only 60 tracks and a 'normal' amount of plugs per track/buss...getting on my pip to be honest