When you upgrade SPS 2003 to SPS 2007 RTM and choose gradual upgrade method with manual database name selection in the new content database that should hold upgraded V3 sites, you get the error;

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An update conflict has occurred, and you must re-try this action. The object SPWebApplication Name=WebSiteName_Pair Parent=SPWebService is being updated by DOMAIN\ACCOUNT, in the OWSTIMER process, on machine SERVER.  View the tracing log for more information about the conflict.
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This happens if you select the check box - 'Manual database' and provide a name which doesn't contain the string '_Pair ' at the end of it.  You can try providig a name with _Pair and this may work.  If not, run the configuration wizard again, disconnect from the existing cnfig db and re-run the wizard to create a new config db and then do the gradual upgrade.