I'm not sure if Garmin have created the forerunners to work like standard memory sticks. The filesystem not available message may be genuine.

At the very least you may need a specific kernel module in order to read from the device, if not a specifically compiled kernel.

You may have some luck compiling garmintools or something like gant, if you can find a version that's compatible with the 301.

That said, I'd be happy to be proven wrong