I tried the exact same DM Script logic that you gave:
PROMPT(TEXT,%BUYERCODE%,"YOU MUST Enter a Single Buyer Code (ex: GA)")
PROMPT(TEXT,%FISYR%,"YOU MUST Enter a Fiscal Year (ex: 2011)")
INFO(%EQU%,=)
INFO(%TAB%,;)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,SUSER,%USER%)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,SAPPSET,%APPSET%)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,SAPP,%APP%)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,TAB,%TAB%)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,EQU,%EQU%)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,LOGICFILENAME,BUYER_ALLOC_REQ_QTY.LGF)
TASK(/CPMB/DEFAULT_FORMULAS_LOGIC,REPLACEPARAM,BUYERCODE%EQU%%BUYERCODE%%TAB%FISYR%EQU%%FISYR%)
Also, used "$BUYERCODE$" - quotes in the logic
And everything else works except the BAPI to actually move the data to a different application (COSTMODEL)
This is my problem logic(see in bold below), it is trying to add a dimension and move the data to that application.
*XDIM_MEMBERSET CURRENCY=LOCAL
*XDIM_MEMBERSET CMACCT=A_VOLUME
*XDIM_MEMBERSET CMDATASRC=DS_BW,DS_MANOVERRIDE
*XDIM_MEMBERSET CMDRIVER=D_NONE
*XDIM_MEMBERSET PRDCNG_COPLANT=P_NONE
*XDIM_MEMBERSET FIN=F_99
*XDIM_MEMBERSET VERSIONBASE=MASTER
*XDIM_MEMBERSET CMVENDOR=BAS(V_DETAILVENDORS)
*XDIM_FILTER TIME=[TIME].PROPERTIES("YEAR")="$FISYR$"
*XDIM_FILTER CMRAW=[CMRAW].PROPERTIES("BUYER")="$BUYERCODE$"
*START_BADI DAPP
DESTINATION_APP="COSTMODEL"
WRITE=OFF
ADD_DIM="CMDATASRC=DS_BW"
*END_BADI
*XDIM_MEMBERSET CURRENCY=LOCAL
*XDIM_MEMBERSET CMACCT=A_VOLUME
*XDIM_MEMBERSET CMDATASRC=DS_BW,DS_MANOVERRIDE
*XDIM_MEMBERSET CMDRIVER=D_NONE
*XDIM_MEMBERSET PRDCNG_COPLANT=P_NONE
*XDIM_MEMBERSET FIN=F_99
*XDIM_MEMBERSET VERSIONBASE=MASTER
*XDIM_FILTER TIME=[TIME].PROPERTIES("YEAR")="$FISYR$"
*XDIM_FILTER CMRAW=[CMRAW].PROPERTIES("BUYER")="$BUYERCODE$"