>>And yes, you got a blank message from me.
>
>Thanks, I sent you the files.

Just a brief conclusion for the curious who may be reading this: denull.prg was building a string from field names (based on a AFields() array), and somewhere around 94th field it got messed up. The string had a regular bunch of "Alter {field} Not Null, ...", except for this one. There it had some binary stuff. In the debugger, the statement "Alter Table (cTable) &clauses Novalidate" caused a syntax error; however, in both VFP 6 and 7 it caused a C0000005 in regular run.

The workaround was not to build such a long string, but rather to generate a .prg, which contained the full Alter Table statements, compile it on the fly and run it.