Pete,
 
You probably know this, the UAD-1 DSP boards haven't been supported for a couple of years. Windows 10 was released well after UAD-1 support ended.  Some drivers/SW/HW, without official Win10 support, may still work on Win10 but could be unreliable. 
 
One other thing, the UAD website says: UAD-1 plug-ins are 32-bit only. You might double check that the current SONAR plug-in path still points to the 32-bit UAD-1 plug-ins. The path name should have something like "\Program Files (x86)\".  If the "x86" is missing, this likely indicates a problem.  You can see this using the Cakewalk Plug-in Manager.  Once again, I'm not familiar with the UAD-1 and this suggestion might not apply. 
 
Here's more info about UAD-1 support on the UA site: https://help.uaudio.com/hc/en-us/articles/206024206-UAD-1
 

earlybirdstudio@aol.com
I am not a computer expert but logic tells me that it seems to be linked with the latest Sonar update. Don't know what your thoughts are on that score?
Pete

A lurking bug in one piece of software can manifest itself after a perfectly valid change is made to surrounding software (i.e. connected or related SW for this example).  Such a bug may stay dormant with other versions of the surrounding software. This may not seem logical, but it happens (as many seasoned engineers can attest).  
 
 Edit: Attempt to clarify plugin path info. 

Hi Tom, Thank you for your input! Had a look at the plug in path and all seems OK. Just a bit miffed if I can no longer use the card as I have several plug ins which were not cheap but not in a position to buy the UAD 2 card!
I have just emailed UA  so will see if they can give me a workaround although they no longer support UAD1 .
Will post when I get a reply!
Pete