Trouble plotting dielectrophoretic forces as a result of particle tracing simulation

Hello all,

I am simulating the motion of particles under a dielectrophoretic force in a microfluidic channel. There are two study steps: one that calculated the E-field and fluid flow field and one that calculates the time-dependent particle trajectories, using the Particle Tracing for Fluid Flow module. My model seems to run fine, and the behavior is what I would expect. However, when trying to plot an arrow surface or arrow volume of the DEP force, I always get the same error:

Failed to evaluate variable.
- Variable: comp1.fpt.Fdpx_deff1
- Geometry: 1
- Domain: 1
Failed to evaluate expression.
- Expression: comp1.fpt.Fdpx_deff1
- Plot: arws1 (Arrow surface)

Does anyone else get this or have any insight as to what the issue is? I don't understand how it can fail to evaluate the variable if it's using it to calculate the particle trajectory...

Thanks, Alisha