You have a good point... He had already known that he failed his tests at that point. I wonder if he was trying to pull a "Mark Hacking" on his family. PVDS was in Holland up until Saturday the 28th of May, his wife stayed in Holland until June 1st. (Joran was left at home in Aruba). The reason they were in Holland is because the mother/wife said there was a family celebration there. But PVDS had just found out he failed his "Judge" exams like a week before Natalee came up missing. Exams are done in Holland.
Why all the lies even about his employment position to Greta?
Do you have any idea if PVDS makes any other kind of living besides 'sitting in' as an occassional judge and studying? Surely he does something else or they've got family money. I doubt AVDS makes enough to support her entire family on a teacher's salary.
Just the fact that he lied is very telling about his personality. At some level, he had to know his failure would eventually come out. Or maybe he's so far in denial that he thought he could keep this a secret. Either way, the lie gives us a window into his personality makeup.