"Unable to perform query" on a java version of ArcGIS Server I also get the error "Please check your parameters"
Here is the ESRI topic at 10 which shows how to_date should be used http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00s500000033000000.htm
Datefield = TO_DATE('yyyy-mm-dd hh:mm:ss','YYYY-MM-DD HH24:MI:SS')
DateTest = TO_DATE('2012-01-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS')
I have also tried not including the time and using / instead of -
Oracle version is 10g. ArcGIS server is version 10 (.net and java tried)