Corrupt Activity Fit File

Try a manual upload from your Garmin device to Garmin Connect Web - How Do I Manually Upload an Activity I Recorded to Garmin Connect?

If you get any message other than Import Complete, then there is a problem with the file. Attach it to this thread. We can take a look to see if it is repairable.

• Zip the file, then in a reply post Insert >> Image/video/file >> click Upload >> browse for file >> OK.
• Or upload the fit file to a reputable file sharing service, such as OneDrive, Google Drive, Dropbox, make the file public, then paste a link to the file in your post.

You can also connect your watch to a computer and browse for the FIT file in TempFIT folder.

If you still cannot locate the appropriate fit file, there's a possibility it was deleted. Check out this thread for recovery options - how do I get my activity back if I delete it?

Fixed using Fit File Repair Tool

Some suggestions to help minimize the occurrence of corrupt fit files:

• Sync your device then remove all activity fit files from your Garmin device using these directions - Removing Recorded Activities on a Garmin Fitness Device 
• Check for firmware updates using Garmin Express

FIT File Tools will fix it. I ran it through the section remover without any adjustments. Upload to Garmin Connect. If necessary, change the activity type.

HRM-Pro, Pro Plus, Tri, and Swim will sometimes corrupt activity fit files 

• Use the HRM download feature only after an activity where it was not possible to wear the watch
• Update the HRM firmware How Do I Update the HRM-Pro Software Using the Garmin Connect App?
• During the HRM-Pro download process keep the strap and watch in close proximity
• If issues persist even after the firmware update, contact Garmin Support
• More here about corrupted HR data: Corrupt FIT File Repair Requests

And congrats on the performance.  

Some suggestions to help minimize the occurrence of corrupt fit files on a Forerunner 35

• Avoid pressing stop or pause during an activity.
• Sync your watch, backup the \GARMIN\ACTIVITY folder, then do a full master reset of your Forerunner 35 using these directions - Restoring All Default Settings.
• Perform a weekly cleanup of the \GARMIN\ACTIVITY folder using these directions - Removing Recorded Activities to Free Up Space. The F35 seems to have problems with longer activities, so this step is important before a longer event.
• Check for firmware updates using Garmin Express.

If you're on a Mac, use OpenMTP to access your device. Note: only one program can access an MTP device at the same time. Close Garmin applications, such as BaseCamp and Express, before using OpenMTP.