Stefan,
Openacs has been ported to PG 7.3 but dotLRN hasn't. What you experience is a call to portal_layout__new with a set of parameters that does not match the data types of the function declaration. PG 7.2 will automatically cast the parameter types in the call to the types of the declaration but PG 7.3 doesn't.
There are bound to be more cases like this. Each would have to be fixed the source code. I'f you feel up for it you could produce patches and submit them in the Openacs bugtracker.
/Bart
