Melodyne 5.3 installed and running fine in standalone but "Edit with Melodyne"in Studio One 4 and 6 just brings up  install dialogue

PluginScan.log shows:

Adding file 4: "file:///C:/Program Files/Common Files/VST3/Celemony/Melodyne/Melodyne.vst3"

Scan next file in scan process: Melodyne

Scan file completed: scan process result = 0x00000000 class data: YES

I have Melodyne.vst3 and MelodyneCore-5.3.1.018.dll in  C:\Program Files\Common Files\VST3\Celemony\Melodyne

Very frustrating. Any ideas? Feel it must be a Studio One issue.

Thanks.