Can't transfer files to external SD after upgrade to Airdroid 4question

Just got the latest update to Airdroid on my phone (Samsung Galaxy S5) and I'm not happy.
Before the upgrade I was able to transfer files from my PC to the external SD card on the phone using the web interface via my PC's browser.
Now when I try to do so, it fails with the message "Network error or permission denied..." and it advises me to check the app permissions on my phone. Well, all the permissions were already enabled, so now what ?

Never mind, finally figured it out - got the answer here: http://forums.androidcentral.com/general-help-how/255566-solved-android-what-do-if-sd-card-mounted-read-only-can-t-write-sd-card.html

Somehow my SD card had gotten some file system errors, which Windows was able to fix. May not have had anything to do with the AirDroid update.