I have blocked ‘something’ & told Comodo to remember my answer… I shouldn’t have, because now Photoshop (CS2) won’t open & keeps telling me…
“An error has been detected with a required application Library and the product cannot continue - Please re-install the product”
I must have blocked Photoshop from accessing something :‘( :’( 
Where can I find what I have done & remove the block?
Many thanks in advance…
Open up Comodo and go to D+/Advanced/Computer Security Policy. Find the program you blocked and right click on it and edit it. Make it trusted. Take time to learn what all the functions and tabs do in Comodo.
Nope… Still doesn’t work
You can also look under the firewall. Go to Firewall/Advanced/Network Security Policy and edit what you blocked. Did you find what you blocked? Did you make it trusted and click apply?
Try to do what Vet said but “Remove” the appropriate entry.This way Defence+ should learn the application again.
Alternatively you may have blocked explorer from running it.
From Computer Security Policy find the %windir%\explorer.exe entry,highlight it and click"Edit" now click “Modify” next to run an executable.You should get a new window with allowed and blocked applications,look under the blocked applications list to see if anything is there.If it is “Remove” it and APPLY to close all windows.
Matty
Also you can remove it like Matty said then reboot.