Hi Niki,
it's the same for me. Downloading of multiple pictures when being connected in a LAN does not work anymore. I get exactly the same error message, as David describes. My Airdroid version is 4.1.5.0, too. I use a Galaxy S4 Android 5.0.1.
I reinstalled Airdroid, but this did not change anything, it still doesn't work. Also I ad a look at the logs you were pointing out, there seems to be nothing special in them. The exception.log shoes an exception of Dec 2014 (strange, since I reinstalled the app - seems like not all files being removed after an uninstall), the mail.log looks like this (2 tries and 2 starts of the app), see below.
To me this looks like a bug, because it has worked fine the last time I used it some weeks ago.
Cheers, Ivo
[left]2017-10-11 20:56:57,357 - [INFO -GCMRegistrationManager] - GCM_ID: , 0, 30214
2017-10-11 20:56:57,358 - [INFO -GCMRegistrationManager] - Account: ,
2017-10-11 20:56:57,516 - [INFO -GCMRegistrationManager] - GCM_ID: , 0, 30214
2017-10-11 20:56:57,517 - [INFO -GCMRegistrationManager] - Account: ,
2017-10-11 20:56:57,531 - [INFO -GCMRegistrationService] - gcmRegistration
2017-10-11 20:56:57,825 - [WARN -CampaignsReceiver] - install referrer: utm_source=google-play&utm_medium=organic
2017-10-11 20:57:04,367 - [INFO -GCMRegistrationService] - GCM Register on Server Succeed.
2017-10-11 20:57:24,841 - [WARN -com.sand.airdroid.servers.managers.event.EventServiceManager] - startEventService
2017-10-11 20:57:29,433 - [INFO -ConnectionConfigHttpHandler] - response = {"data":{"lab":{"enable_connection_update":true,"enable_forwardurl_refresh":true}},"msg":"","code":1}
2017-10-11 20:57:29,433 - [INFO -ConnectionConfigHttpHandler] - response.enable_forwardurl_refresh = true
2017-10-11 20:57:29,434 - [INFO -ConnectionConfigHttpHandler] - response.enable_connection_update = true
2017-10-11 20:58:05,908 - [INFO -AirDroidService] - cause by stop code 6
2017-10-11 21:03:15,182 - [INFO -GCMRegistrationManager] - GCM_ID: eKilaLySIX0:APA91bH01WZN7RtyTtJj9WpiXMX_NWYPGBm3TKBEamLRWe3PttBTTmyCEmzrrS-p4-0aEZKVMI1F9fCAW1tQgIq5M_tp2T9NNp2ngoFp2H6oZXi_gb3VvW7w2JrwdAMj4PdjOjoYvxPz, 30214, 30214
2017-10-11 21:03:15,204 - [INFO -GCMRegistrationManager] - Account: ,
2017-10-11 21:03:15,280 - [INFO -GCMRegistrationManager] - GCM_ID: eKilaLySIX0:APA91bH01WZN7RtyTtJj9WpiXMX_NWYPGBm3TKBEamLRWe3PttBTTmyCEmzrrS-p4-0aEZKVMI1F9fCAW1tQgIq5M_tp2T9NNp2ngoFp2H6oZXi_gb3VvW7w2JrwdAMj4PdjOjoYvxPz, 30214, 30214
2017-10-11 21:03:15,280 - [INFO -GCMRegistrationManager] - Account: ,
2017-10-11 21:03:15,323 - [INFO -GCMRegistrationService] - gcmRegistration
2017-10-11 21:03:16,956 - [INFO -GCMRegistrationService] - GCM Register on Server Succeed.
2017-10-11 21:03:20,247 - [WARN -com.sand.airdroid.servers.managers.event.EventServiceManager] - startEventService
2017-10-11 21:04:50,291 - [INFO -AirDroidService] - cause by stop code 6[/left]