Hello Neks, I' trying to solve the MHD equations and encounter the same error reported here: http://lists.mcs.anl.gov/pipermail/nek5000-users/2011-June/001365.html. For testing, I have set up a small grid (384 elements) with B=0 at the boundaries and B=0 as initial conditions, and the error appears before the first timestep. As mentioned in the documentation, I have used the same BC-types for the B Field as for the velocity, so in the .rea file it reads: 5909 ***** PASSIVE SCALAR 1 BOUNDARY CONDITIONS ***** 5910 E 1 1 0.00000 0.00000 0.00000 0.00000 0.00000 5911 E 1 2 0.00000 0.00000 0.00000 0.00000 0.00000 5912 V 1 3 0.00000 0.00000 0.00000 0.00000 0.00000 5913 E 1 4 0.00000 0.00000 0.00000 0.00000 0.00000 5914 E 1 5 0.00000 0.00000 0.00000 0.00000 0.00000 5915 E 1 6 0.00000 0.00000 0.00000 0.00000 0.00000 5916 E 2 1 0.00000 0.00000 0.00000 0.00000 0.00000 5917 E 2 2 0.00000 0.00000 0.00000 0.00000 0.00000 5918 E 2 3 0.00000 0.00000 0.00000 0.00000 0.00000 5919 E 2 4 0.00000 0.00000 0.00000 0.00000 0.00000 5920 E 2 5 0.00000 0.00000 0.00000 0.00000 0.00000 5921 E 2 6 0.00000 0.00000 0.00000 0.00000 0.00000 5922 E 3 1 0.00000 0.00000 0.00000 0.00000 0.00000 5923 E 3 2 0.00000 0.00000 0.00000 0.00000 0.00000 5924 E 3 3 0.00000 0.00000 0.00000 0.00000 0.00000 5925 E 3 4 0.00000 0.00000 0.00000 0.00000 0.00000 5926 E 3 5 0.00000 0.00000 0.00000 0.00000 0.00000 5927 E 3 6 0.00000 0.00000 0.00000 0.00000 0.00000 5928 v 4 1 0.00000 0.00000 0.00000 0.00000 0.00000 5929 E 4 2 0.00000 0.00000 0.00000 0.00000 0.00000 5930 E 4 3 0.00000 0.00000 0.00000 0.00000 0.00000 etc. The thread above mentioned that it was due to incorrect BCs, but unfortunately no more details were given. Cheers, Jan