JanKusanagi at

Ah, that ancient version explains why it's having trouble reading the error message. Pump.io 4.0 changed a few things on how error messages are reported.

Supporting that is actually one of the improvements in the changelog for 1.4.0, so 1.3.7 wouldn't help with this.

You could try running from a command line with the --debug parameter (besides whatever parameters you already use, like --nohttps of course). The error could probably be read in the console output.