Kingfisher(IT) can be used for a global explorer ticket but not a oneworld explorer.
0. APPLICATION AND OTHER CONDITIONS
First/Business/Economy travel valid for RTW /Open Jaw travel via
AA /AS /AY /BA /CX /EI /FJ /GF /IB /IG /IT/JC /JL /JO /KA /LA /LP /MA /MX /NU /QF /RJ/S7 /XL /4M
http://www.oneworld.com/content/libr...are%20rule.pdf
If the OP is trying to plan a global explorer(for which you can use IT) then the oneworld online tool is not programmed to do that(and will not show IT flights). The online tool is only for planning/booking a oneworld explorer ticket(for which IT is not an authorized airline).
If the OP is starting in BRU(the routing as others have noted is not entirely clear) then he may be running afoul of the two stopovers in continent of origin rule or the limited sectors from LHR rule.