To use some of Seesaw's tools, like the video upload tool, you must allow third-party cookies and site data in your browser settings.
- On your computer, open Chrome
- Go into Preferences or click on More
- Go into Settings
- Click on Show advanced settings
- In the "Privacy" section, click on Content settings
- Uncheck the "Block third-party cookies and site data" option
- Refresh your browser window to reload your new preferences
Here's an FAQ from Google about this issue.