This one is very odd. 
I'm a Steam user having upgraded from MC6T.
Despite a full PC reboot Sonar X3 can't find my Cakewalk Soundcenter at all.
MC6T finds it no problem but not X3.
It was working fine (including seeing all my DSF expansions) until I fired it up this morning.
I know there was meant to be a Steam fix coming out for the 'Some X3 users not getting MC6T expansion packs in Soundcenter' issue but has this now broken Souncenter generally for X3 users?
All my other (55) VSTs (including Cakewalk ones like Rapture) fire up with no issues.

Hi Andy. If you haven't already done so please update to X3D and then perform a VST reset (not just rescan).
Also check the plugin manager (under "Manage Layouts").
 
Also check you have the path for sound centre plugin correctly configured.
Please note Sound Centre is a 32 bit VST.
 
Thanks

Did this - makes no difference.
 
Also I'm on Steam with auto updates on, so assume I have updated to X3D already.
 
 

"Help - About" will confirm this.
Please find out where the plugin DLL is on your hard drive. Sorry I dont have the DLL name to hand right now so you could search for it on your hard drive. Google may reveal the dll name.

OK fixed now - I pointed the VST scans to the specific Cakewalk Sound Center folder and it's found it again - no idea why it lost it.
 
FIXED
 

Excellent. The file path clearly wasn't there. Glad you got it sorted. Cheers...