easy fix, unplug the charge wire/clip from computer, turn off your watch, connect the charge wire to the watch, hold the top right button, don't let go, plug the wire to the computer continuing to hold…
I'm having the same issue.. Win 10. Garmin 235 Has worked perfectly... I do believe I have installed the Win 10 service pack since last sync though..... ANyone have ideas?
You can use CHKDSK or Check Disk Utility to check for issues:
Take note of the drive letter in the error e.g. “You need to format the disk in drive H: before you can use it, do you want to format it”. Your external hard drive letter is H. Right-click on the Start Menu and select Command Prompt or type “cmd” and hit Enter to run it as administrator. In the pop-up command window, type “chkdsk drive letter:f”, since your drive letter is “H”, then simply type “chkdsk H:f” and hit Enter.
If you don't want to lose the data, I suggest you recover the data before fixing the issue or formating the disk. You can try Bitwar Data Recovery to retrieve the data on the disk, and save the data to another device. Then you can try to format the disk to solve this error.
I get the "format the disk" comment too, in January 2020. I'm a Windows insider getting updates to Win 10 Education (similar to Pro). The message seems to do no harm other than I can't access my files to clean out old clutter. I'm also having difficulty syncing today. Since writing this message, I've charged my watch to give it more power (2 out of 4 bars). Since I had a Windows update today, I turned off my computer and restarted it. My cell phone is fully charged. Anyway, a reboot of my recently updated Win 10 Education computer got my watch to sync for total steps but I lost all my recent activities (runs with miles and HR).
I have no solution but the same problem. for details see forums.garmin.com/.../usb-disk-requires-formatting-when-connecting-forerunner-to-laptop-any-advice