Just curious, does your parts.ini file look something like this? I seem to recall that I had to edit mine back in the day to include both library styles. [Funny, I see that mine is slightly wrong.]
[PartsAssembler]
MenuItems=58
Menu1=Body 1,F1.BMP,F1\F1
Menu2=Body 2,F2.BMP,F2\F2
Menu3=Ship 1,S1.BMP,S1\S1
Menu4=Ship 2,S2.BMP,S2\S2
Menu5=Wing 1,W1.BMP,W1\W1
Menu6=Wing 2,W2.BMP,W2\W2
Menu7=Asymmetry,SD.BMP,SD\SD
Menu8=Engine,EG.BMP,EG\EG
Menu9=Cockpit,CP.BMP,CP\CP
Menu10=Bridge,BR.BMP,BR\BR
Menu11=Battery 1,G1.BMP,G1\G1
Menu12=Battery 2,G2.BMP,G2\G2
Menu13=Tank,TK.BMP,TK\TK
Menu14=Shield,SL.BMP,SL\SL
Menu15=Joint,JT.BMP,JT\JT
Menu16=Building,BL.BMP,BL\BL
Menu17=Background,BG.BMP,BG\BG
Menu18=Animal,AN.BMP,AN\AN
Menu19=Robot,RB.BMP,RB\RB
Menu20=Basic 1,P1.BMP,P1\P1
Menu21=Basic 2,P2.BMP,P2\P2
Menu22=Basic 3,P3.BMP,P3\P3
Menu23=Basic 4,P4.BMP,P4\P4
Menu24=Simple 1,T1.BMP,T1\T1
Menu25=Misc 1,OT.BMP,OT\OT
Menu26=Misc 2,O2.BMP,O2\O2
Menu27=Special Effect,EF.BMP,EF\EF
Menu28=Character 1,C1.BMP,C1\C1
Menu29=Character 2,C2.BMP,C2\C2
Menu30=Character 3,C3.BMP,C3\C3
Menu31=Kanji,KJ.BMP,KJ\KJ
Menu32=Head,kao.bmp,kao\kao
Menu33=Eye,eye.bmp,eye\eye
Menu34=EyeBrow,mayu.bmp,mayu\mayu
Menu35=Mouth,kutsi.bmp,kutsi\kutsi
Menu36=Nose,hana.bmp,hana\hana
Menu37=Ear,mimi.bmp,mimi\mimi
Menu38=Hair,kami.bmp,kami\kami
Menu39=Hand,Te.bmp,Te\Te
Menu40=Male,man.bmp,man\man
Menu41=Female,woman.bmp,woman\woman
Menu42=RobotHead,rohead.bmp,rohead\rohead
Menu43=RobotBody,robody.bmp,robody\robody
Menu44=RobotArm&Leg,roarm.bmp,roarm\roarm
Menu45=RobotHand&Foot,rohand.bmp,rohand\rohand
Menu46=RobotEtc,roetc.bmp,roetc\roetc
Menu47=Armor,armor.bmp,armor\armor
Menu48=Weapon,weapon.bmp,weapon\weapon
Menu49=Fang,fang.bmp,fang\fang
Menu50=Nozzle,nozzle.bmp,nozzle\nozzle
Menu51=Rock,rock.bmp,rock\rock
Menu52=U8,u8.bmp,u8\u8
Menu53=U9,u9.bmp,u9\u9
Menu54=Exp1,exp1.bmp,exp1\exp1
Menu55=Exp2,exp2.bmp,exp2\exp2
Menu56=Exp3,exp3.bmp,exp3\exp3
Menu57=BUILDING1,BUILDING1.BMP,BUILDING1\BUILDING1
[PartsAssembler.jpn]
Menu1=Body 1,F1.BMP,F1\F1
Menu2=Body 2,F2.BMP,F2\F2
Menu3=Ship 1,S1.BMP,S1\S1
Menu4=Ship 2,S2.BMP,S2\S2
Menu5=Wing 1,W1.BMP,W1\W1
Menu6=Wing 2,W2.BMP,W2\W2
Menu7=Asymmetry,SD.BMP,SD\SD
Menu8=Engine,EG.BMP,EG\EG
Menu9=Cockpit,CP.BMP,CP\CP
Menu10=Bridge,BR.BMP,BR\BR
Menu11=Battery 1,G1.BMP,G1\G1
Menu12=Battery 2,G2.BMP,G2\G2
Menu13=Tank,TK.BMP,TK\TK
Menu14=Shield,SL.BMP,SL\SL
Menu15=Joint,JT.BMP,JT\JT
Menu16=Building,BL.BMP,BL\BL
Menu17=Background,BG.BMP,BG\BG
Menu18=Animal,AN.BMP,AN\AN
Menu19=Robot,RB.BMP,RB\RB
Menu20=Basic 1,P1.BMP,P1\P1
Menu21=Basic 2,P2.BMP,P2\P2
Menu22=Basic 3,P3.BMP,P3\P3
Menu23=Basic 4,P4.BMP,P4\P4
Menu24=Simple,T1.BMP,T1\T1
Menu25=Misc 1,OT.BMP,OT\OT
Menu26=Misc2,O2.BMP,O2\O2
Menu27=Special Effects,EF.BMP,EF\EF
Menu28=Character 1,C1.BMP,C1\C1
Menu29=Character 2,C2.BMP,C2\C2
Menu30=Character 3,C3.BMP,C3\C3
Menu31=Kanji,KJ.BMP,KJ\KJ
Menu32=Head,kao.bmp,kao\kao
Menu33=Eye,eye.bmp,eye\eye
Menu34=Eyebrow,mayu.bmp,mayu\mayu
Menu35=Mouth,kutsi.bmp,kutsi\kutsi
Menu36=Nose,hana.bmp,hana\hana
Menu37=Ear,mimi.bmp,mimi\mimi
Menu38=Hair,kami.bmp,kami\kami
Menu39=Hand,Te.bmp,Te\Te
Menu40=Male,man.bmp,man\man
Menu41=Female,woman.bmp,woman\woman
Menu42=Robot Head,rohead.bmp,rohead\rohead
Menu43=Robot Body,robody.bmp,robody\robody
Menu44=Robot Arm&Leg,roarm.bmp,roarm\roarm
Menu45=Robot Hand&Foot,rohand.bmp,rohand\rohand
Menu46=Robot Etc,roetc.bmp,roetc\roetc
Menu47=Armor,armor.bmp,armor\armor
Menu48=Weapon,weapon.bmp,weapon\weapon
Menu49=Fang,fang.bmp,fang\fang
Menu50=Nozzle,nozzle.bmp,nozzle\nozzle
Menu51=Rock,rock.bmp,rock\rock
Menu52=U8,u8.bmp,u8\u8
Menu53=U9,u9.bmp,u9\u9
Menu54=Exp1,exp1.bmp,exp1\exp1
Menu55=Exp2,exp2.bmp,exp2\exp2
Menu56=Exp3,exp3.bmp,exp3\exp3