Invalid Bounding Box Error

I am working on the SEFT tutorial and am changing the ultrasound transducer frequency from 550kHz down to 2khz. When I do this, I get a bounding box error: 'Voxeler was unable to finish due to the following error: Invalid bounding box'.
Is there any guidance around what is and isn't an acceptable bounding box?

2kHz will probably not be feasible in most propagating media, because the wavelength will simply be too large compared to the grid resolution your geometry requires (leading to unreasonably large time steps).
You might want to check for e.g. what your grid look like, especially the padding at the boundaries of your computational domain.