fixed parse behaviour.

the parser error messages from sub functions were thrown away and
replaced by an impractical error message. Furthermore, non-required
blocks were automatically treated as comments, if there occurred any
parse error. This commit changes this behavior such that in case the
block name (e.g. VAR, RULES, DATATYPES, etc) was parsed correctly the
parser expects a valid block. In case an error gets thrown in this block
the parser stops.