During the simulation of an Functional Mock-up Unit (FMU) generated from Matlab Simulink in PowerFactory the simulation start time needs to be set to zero (start time [attribute tstart] in the page Step Size in the command: Calculation of initial conditions). Otherwise, an error stating "Initial conditions invalid" is printed in the output window. This requirement is from the Simulink exported FMU, and FMUs from other tools may allow for different starting times.