Multiple instances
While trying to run two instances of ocl-plus last version I got :
ERROR: already an instance C:\oclHashcat-plus-0.12\oclHashcat-plus64.exe running on pid xxx

Atom, I would suggest to let the user choose if multiple instances can run, via a parameter for example.
Yea, that pissed me off once, too.
Even --force didn't help.

-1 for this.
Guys, read the release notes. This is just like trying to run two JTR instances at the same time: you need to specify a different session name for each.

Quote:Support added for sessions.

The introduction of restore/resume support also introduces the challenge of running multiple concurrent instances of oclHashcat-plus, as each instance would attempt to store its progress to the same restore file. This challenge has been addressed by adding support for named sessions.

When using the "--session <name>" parameter, each instance writes its progress to its own restore file, rather than the default restore file. To restore a named session, simply tell oclHashcat-plus which session to restore:

./oclHashcat-plus64.bin --restore --session mysession

A named session can also be created from a default session upon exiting oclHashcat-plus. For example, if you start oclHashcat-plus without the --session parameter and later choose to exit the application to work on a more important job, you can stop the process by pressing 'q' like normal, and rename "oclHashcat-plus.restore" to "<session_name>.restore" before running the other job. This will allow you to resume your previous job using "--session <session_name>" at a later time.
Interesting. Somehow, I missed that.

Perhaps rephrasing the error's massage would have helped in preventing such misunderstanding. Something like:
ERROR: oclHashcat-plus.restore is already in use (pid 000000), please use another session name to run.
Replacing oclHashcat-plus.restore with the binary's default restore file name and 000000 with the actual pid.

And +2 for sessions!