Bibtex errors and warnings

/tmp/roee.bib, line 1, warning: overriding existing definition of macro "jcomputing"
/tmp/roee.bib, line 2, warning: overriding existing definition of macro "jdm"
/tmp/roee.bib, line 3, warning: overriding existing definition of macro "jcss"
/tmp/roee.bib, line 4, warning: overriding existing definition of macro "jsiam"
/tmp/roee.bib, line 5, warning: overriding existing definition of macro "jacm"
/tmp/roee.bib, line 6, warning: overriding existing definition of macro "jalg"
/tmp/roee.bib, line 7, warning: overriding existing definition of macro "comacm"
/tmp/roee.bib, line 8, warning: overriding existing definition of macro "ipl"
/tmp/roee.bib, line 9, warning: overriding existing definition of macro "orl"
/tmp/roee.bib, line 10, warning: overriding existing definition of macro "dam"
/tmp/roee.bib, line 11, warning: overriding existing definition of macro "mor"
/tmp/roee.bib, line 12, warning: overriding existing definition of macro "proc"
/tmp/roee.bib, line 13, warning: overriding existing definition of macro "approx"
/tmp/roee.bib, line 14, warning: overriding existing definition of macro "esa"
/tmp/roee.bib, line 15, warning: overriding existing definition of macro "focs"
/tmp/roee.bib, line 16, warning: overriding existing definition of macro "latin"
/tmp/roee.bib, line 17, warning: overriding existing definition of macro "podc"
/tmp/roee.bib, line 18, warning: overriding existing definition of macro "sagt"
/tmp/roee.bib, line 19, warning: overriding existing definition of macro "soda"
/tmp/roee.bib, line 20, warning: overriding existing definition of macro "spaa"
/tmp/roee.bib, line 21, warning: overriding existing definition of macro "stoc"
/tmp/roee.bib, line 22, warning: overriding existing definition of macro "stacs"
/tmp/roee.bib, line 23, warning: overriding existing definition of macro "icalp"
/tmp/roee.bib, line 24, warning: overriding existing definition of macro "mobihoc"