No, you do not need to trash anything that you have done in Sib 5.
If ALL you need to do is write, as in you don't need any playback, you can use a Playback Configuration that doesn't have any instances of anything at all. You wouldn't have to wait for sounds to be loaded and you'll still get all of the notation you want in the score. Anyway, another option. (I'm sure you do want playback though.)
Now that I'm seeing the error message in the image you attached, I'm remembering that this shows up when KP2 can't find the patch file it's looking for. From Sibelius, go to Play > Playback Devices, select any KP2 instance from the Active Devices list (on the right), click on the Show button. From the KP2 UI, click on the Info button in the VDL block, then make sure that the Library Installation Path points to where you installed the VDL sounds. (Images attached) Most people using a Mac have it installed in Macintosh HD:Applications:Tapspace:Virtual Drumline 2.5.
If this doesn't fix it, then do a double check that all of the instruments you have in the score are from the appropriate ensembles.
Let us know