I've had this problem for the last oooh, 10 years or so. I think I've finally found why its happening.
I've posted many times on the issue I've read tons of posts here and elsewhere, my guess is there's lots of people who have just given up trying to use it.
I notice in resource monitor that photoshop's status goes to "not responding" when the action is playing. So it seems pretty clear that the items that are in the queue to be sent to photoshop are getting sent too early, and that the droplet is finding photoshop unavailable.
I spent a bit of time with an adobe tech on this, but he couldn't recreate the issue. If anyone else who suffers from this issue would care to check their resource monitor whilst running the droplet, I'll collate the info and submit it to adobe...
One more time....
edit: I "analysed the wait chain". Which doesn't mean much to me, but I can see a bunch of threads in "waiting status". I dont know if this is relevant but here it is
Ha ha, Droplet not communicating...for ever it seems. I'm using CS4 with W7, had my share of trouble with this, just now found a 7years old closed thread about it - But I'm not satisfy with the proposed solutions.
The reason is that I keep getting this msg but so far simply restart PS and it works again! I'm here because I was curious to see if there was a definitive reason or fix for this.
So far I feel lucky this works but would not mind not having the problem although it simple enough to restart PS.
To explain further I already run PS and actually used my 70% reduction Droplet for entire photo folders. Then all of the sudden it decides not to communicate anymore when I drop another lot of pics into it.
I don't either bother about administrator right as in the past in did not help. And other 'would be' solution with UEA etc. are obviously not the issue if restarting the program is successful. When I say obviously perhaps I'm wrong but it's what it seems to be for me.
So all I can say, try to restart PS else your situation may be different than mine, and I don't know what is my situation! Just this works for me.