Garmin 910XT ERROR when uploading on Garmin Express

Hello guys!
In my case, aparently I have solved it.....I have removed old activities, for test I have created new and in historical data transfer all.....(here i have no the watch...)
One friend has 310XT, he told me that is common issue...
I hope it works.
Good luck!

I'm still having issues with Garmin connect and my 910xt. I was able to upload a new file this morning, but cannot do a manual upload of old files for which uploads have failed in the past two days. Is anyone from Garmin monitoring this site?

Have you tried to do Transfer all?

I too have a 910XT who after 1.November has behaved totally wayward with my Mac. One 17km run is just "gone"... God knows where. Now, nothing works as it has been and the worse is that it's seems like Garmin has upgraded all this trouble our way... I don't know if it's ignorance or greed to expect us all to upgrade our systems..., but the company has lost stars in my book. My 910XT is less than two years old with me and has worked fine on my computer. Why force me into upgrading to something that DOES NOT WORK on my Mac!? The "Modern" Garmin Connect is very poor IMO. At least the old one did a basic job to be expected, if somewhat underwhelming. The new GC doesn't seem to be made by people who workout on a regular basis (or know people who does...), it's that bad.

By the look of all the unsatisfied users in this forum, someone like Strava will SWALLOW Garmins endurance dep. for breakfast in the future over night. I will definitely check out the competition for my next HR monitor.

I've had this problem too - activities between 27 October-02 November won't upload (though are still on the watch) but newer workouts transfer correctly. There are no .fit files for the missing workouts.

Any advice welcome!

I have found that each time I ride at the velodrome (outdoor) my Garmin upload has failed. It worked on rides before and after, fine for runs and swims. I am frustrated because I wanted the HR data from a tough training session. I can't find that the file is saved anywhere on my computer. I have a Mac Book Air and i am using Garmin Express.

Anyone know how to identify a corrupt .fit file? Does Garmin label the files that doesn't work differently or simply delete them?
Loosing workouts is just too annoying! (I am sure I pressed the stop button and quite sure I pressed Reset)

ditto here on symptoms --- 910xt. same 1989 activity, plus 135 items with time stamp at the time i'm on computer. sync says >> 3hrs.... and when I stop sync -- watch doesn't show that there is even an exercise from yesterday (i know i ran 5 miles, and i know I saved it......)

Same issue; I have lost 3 of 4 workouts and data since Sunday, Nov 2. Today on GarminConnect I get the page header, sidebar, and NO (NONE) of my data from the last several months.

Garmin Tech Team - are you reading these comments??? !!!

Colleagues,
I just got off the phone with Garmin Fitness tech support and got all of my activities reloaded correctly. If you are still having this issue - I would suggest call in.