I would call your demonstrator or HO for some advice Kellie. Hopefully another member might know what caused this to happen.
Just looked in the manual and it says this
Trouble with Scales: "Check: while pressing tara button do not touch Thermomix; nothing leans against Thermomix; no tension on the cable; Thermomix ”feet“ are clean; worktop is clean, solid, even and not vibrating; do not slide Thermomix over the worktop."