1) Your FrostWire was working fine until you've updated the Android operating system
2) You are sure your internet connection is fast/stable enough & it is not blocking/throttling BitTorrent traffic
3) You have been saving to SD Card
4) ALL your downloads end up producing an Error, the below solutions might work for you.
They all have to do with FrostWire not being able to save to your SD Card and the easiest way to test if this is actually the reason (and not your internet connection), is to switch to internal memory and try downloading something.
If you have updated to Android 4.4 - KitKat:
Close FrostWire and all other applications, just to be safe.
Go to your phone's Settings > More > Storage scroll down and Unmount SD Card. Then mount it again.
Open FrostWire and try downloading again.
If you have updated to Android 5.0 - Lollipop:
You most likely only have to chose a download location again.
Settings > Storage Location
Because Android has been changing the way Apps are allowed to save to SD Card between versions, your previous location might not be accessible to FrostWire any longer or it might be simply named differently...
If you have updated to Android 6.0 - Marshmallow:
You most likely have to grant FrostWire specific permissions to access your SD Card. You should have been prompted when first using FrostWire after an update, but if you haven't go to your Storage Location Settings pick internal memory and switch back to SD Card to bring up the pop up again.
Settings > Storage Location > Internal Memory
Settings > Storage Location > SD Card
Tap OK on Permission PopUp
To edit/adjust Permissions granted to the apps on your device, go to
Device Settings > Apps > FrostWire > Permissions > Storage
While on Storage, you can also tap on the 3 menu dots in upper right corner to show all permissions and make sure 'read the contents of your SD card' is granted.