Time Machine stuck on "Preparing Backup"

Hi,

In preparation to install Bootcamp, i have tried to make a Time Machine backup on a partitioned external SSD. However, Time Machine will be stuck on "Preparing Backup". It's been preparing for over an hour now.

I have already tried the following:

• Remove the inProgress file
• Stop and restart the backup
• Run Disk Utility First Aid

My question is:

What can i do to fix it?