I am also seeing this, and as Garmin Connect Mobile won't work, crashing constantly, it means that I can't record a weight at all.
Any hints on a solution appreciated. I have tried updating my Account Settings, and can't think of anything else to try. Appears to be a problem with the field validation.
I had just changed my Display Preferences / Number Format this morning as I noticed numbers were using a comma (,) instead of a period (.), so I thought I may have caused the issue and tried page refreshes etc.