You need to offer some more detail. What version of LR and Photoshop( what version of ACR Plugin installed in Photoshop)?
Are you seeing any warning dialog? If not go to Lightroom > Preferences> General Tab> Click on "reset all warning dialogs".
LR 5.6 64-bit - all updates processed successfully
PS 13.0.1 64-bit - all updates processed successfully
Windows 7 / Version 6.1
do not understand "ACR Plugin" (what is that)? According to Adobe, this Plugin is not on the list of Adobe offered plug-ins for CS6
did reset warning dialogs just now
following warnings were displayed after about 1 min after ENTER:
THE RECORD COULD NOT BE PROCESSED AS ADOBE PHOTOSHOP CS6 COULD NOT BE STARTED
warning displayed again after entering OK, then after second OK:
LR COULD NOT PREPARE THE RECORD FOR PROCESS - THE RECORD WILL NOT BE OPENED
(translated from German to English)
I have to add:
after pressing OK for the warnings, sometimes (only sometimes) photoshop is opened correctly. mind: after approx. one minute waiting time for the warnings.
Also what file type are you sending to PS. You say Photos how many? Is the problem something new? Did it function previously?
Plug-in Camera Raw Version: 126.96.36.199
I send one photo at the time with the file type jpg or cr (Canon Camera Raw). It worked previously - but I am not sure whether it has to do with the upgrade to Version 5.6.