In the Unoffical Alternate Artworks .datfile, you have an entry "default" that is the .7z zip file of all of the artwork. I believe this should be removed from the datfile.
machine name="default"
rom name="artworks_alt_229-fullset.7z.001" size="524288000" crc="f6bfeab9" sha1="f936927da288f2d35e6733adf908a1823e15632e" rom name="artworks_alt_229-fullset.7z.002" size="524288000" crc="9856d42c" sha1="8c7082f01f4d0874261b16b38032ab53c3312e2a" rom name="artworks_alt_229-fullset.7z.003" size="524288000" crc="ff284541" sha1="78bfe1ce23d274dd1bc8c060ca2b77eadb2d14b1" rom name="artworks_alt_229-fullset.7z.004" size="524288000" crc="b651d689" sha1="e8dd6472dcb92260b1c27ca925512eead8564f51" rom name="artworks_alt_229-fullset.7z.005" size="11350215" crc="8bbcaf5d" sha1="54d2826e7b22b0d8bc8839301b13d695ed042488"