DBX says "Can't write to process" !

[mario%ntiaa.embrapa.ansp.br at uicvm.uic.edu]

Wizards,

I've got a problem with dbx(1). When I try:
        dbx my_bin
it replies:
        Can't write to process (0xaaaaa)
Where aaaaa == octal address. If I try it again 3 or 4 times it works,
BUT all breakpoints previously set are "forgotten".  If I ask "where",
I can see it didn't begin execution. I couldn't find any thing about
that in the MAN pages.
Any hint is REALLY appreciated. I can summarize replies and re-post
it later.

Mario.
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