Problems with switching to individual head model
From BESA® Wiki
This Wiki page provides solutions for common issues when trying to activate the individual head model in BESA Source Analysis.
I get an error message when selecting the individual EEG BEM or FEM model in Source Analysis
Reference electrode
A possible reason is that a reference electrode is defined, but was not digitized. In that case: Close BESA Source Analysis. In BESA Research, select Edit / Channel Configuration. In the channel configuration, switch off the reference electrode. After accepting with OK, re-start BESA Source Analysis. Now it should work as expected.