Check the following to ensure that your attachements are sending and receiving properly:

1. Ensure you have an updated version of the software.
2. Verify your internet connection is stable.
3. Try disabling any anti-virus software temporarily.
4. Restart your computer and try sending the attachment again.
5. Re-upload the document after saving it in the correct file format.
6. Make sure your browser is configured to accept certain file types.