You have to make sure that the foot pedal is compatible. You can check the list here: http://help.nchsoftware.com/help/en/scribe/win/inpdev-compatible.html and foot pedal driver must be detected by your operating system with the driver for the set up to continue.
Does the issue occur in other files? Have you tried other MP3 files? You may want to try reinstalling Express Scribe, doing so will require you your installer and registration code.
You can try to enable Express Scribe mini while working on MS Word. Click on View then select "Float Above Other Windows" and "Show Express Scribe Mini Control" - you can also use the shortcut key CTRL+M.
If you are using Express Scribe on the computer, you can try to delete old dictations. Follow the folder path listed in Disk Usage tab. Reinstalling Express Scribe will also help.
Try to uninstall Express Scribe. Uninstall the audio driver. Restart your computer. Reinstall audio driver and Express Scribe.
If the issue exist, open a support ticket here: https://www.nch.com.au/support/supportcontact.html?software=Scribe&support
You may consider reinstalling Express Scribe. Contact support for more help here: https://www.nch.com.au/support/supportcontact.html?software=Scribe&support=https%3A%2F%2Fwww.nch.com.au%2Fscribe%2Fsupport.html&pty=2&purchaseclass=scribe&dldwin=https%3A%2F%2Fwww.nch.com.au%2Fcomponents%2Fessetup.exe&dldmac=https%3A%2F%2Fwww.nch.com.au%2Fcomponents%2Fscribemaci.zip
Is this the only video file you are having trouble with? Express Scribe Pro works for both video and audio, you have to make sure that you have this license.
You have to make sure that you have the licensed version for video format to work. Also, you can open a support ticket here: https://www.nch.com.au/support/supportcontact.html?software=Scribe&support
To register, you may open the program, click on any menu at the upper left-hand corner, select Register Software.., enter the registration code and click on Register. OR click "Enter Code if you have already purchased".