Why is this statement occurring as "Invalid use of Null"

PARAMETERS START_DATE DateTime, END_DATE DateTime, STATE Short;
INSERT INTO INVENTORY ( FILENO, FORW_NO, CRED_NAME, FORW_FILENO, FORW_REFNO, PLAINTIFF_1, PLAINTIFF_2, PLAINTIFF_3, PLAINTIFF_4, PARA, COLLECTOR, NAME, STREET, STREET2, CITY, ST, ZIP, RET_MAIL, SSN, PHONE, FAX, EMP_NO, DATE_RECD, [#_ACCTS], ORIGINAL_CLAIM, BAL, LPAYMNT_DATE, LPAY_AMT, BKCY_CHAPTER, BKCY_FILENO, BKCY_FILED_DATE, ADVA, DOCKET_NO, DSMIS_DATE, SUIT_DATE, SERVICE_DATE, AF_DATE, JMT_DATE, JMT_AMOUNT, GARN_DATE, COST_EXPENDED, PRIN_COLLECTED, INT_COLLECTED, COST_REC, STAT_EARNED, PRIORITY, MATRIX_ID, [STAT1 CODE], STAT1_DATE, DATE_DEBT, PRE_J_RATE, [AMT OF 1ST MORTGAGE], [AMT OF 2ND MORTGAGE], MISC_CMT4, PAID_TO_DATE, LST_PMT_RANGE, [%_PAID], TOTAL_INT, TOTAL_DUE, STATUTE, SOL_DT )
SELECT dbo_Master.FILENO, dbo_Master.FORW_NO, dbo_Master.CRED_NAME, dbo_Master.FORW_FILENO, dbo_Master.FORW_REFNO, dbo_Master.PLAINTIFF_1, dbo_Master.PLAINTIFF_2, dbo_Extra.PLAINTIFF_3, dbo_Extra.PLAINTIFF_4, dbo_Master.PARA, dbo_Master.COLLECTOR, dbo_Debtor.NAME, dbo_Debtor.STREET, dbo_Debtor.STREET2, dbo_Debtor.CITY, dbo_Debtor.ST, Left(Trim([zip]),5) AS [ZIP-5], dbo_Debtor.RET_MAIL, dbo_Debtor.SSN, dbo_Debtor.PHONE, dbo_Debtor.FAX, dbo_Master.EMP_NO, dbo_Master.DATE_RECD, IIf([dbo_master.fileno] Is Not Null,1,"") AS [#_ACCTS], CCur([ORIG_CLAIM]) AS ORIGINAL_CLAIM, CCur([BALANCE]) AS BAL, dbo_Master.LPAYMNT_DATE, CCur([LPAYMNT_AMT]) AS LPAY_AMT, dbo_Debtor.BKCY_CHAPTER, dbo_Debtor.BKCY_FILENO, dbo_Debtor.BKCY_FILED_DATE, dbo_Master.ADVA, dbo_Master.DOCKET_NO, dbo_Debtor.DSMIS_DATE, dbo_Master.SUIT_DATE, dbo_Debtor.SERVICE_DATE, dbo_Debtor.AF_DATE, dbo_Master.JMT_DATE, CCur([dbo_Master.JMT_AMT]) AS JMT_AMOUNT, dbo_Debtor.GARN_DATE, CCur([COST_EXP]) AS COST_EXPENDED, CCur([PRIN_COLL]) AS PRIN_COLLECTED, CCur([INT_COLL]) AS INT_COLLECTED, CCur([COST_RECOVERED]) AS COST_REC, CCur([STAT_EARN]) AS STAT_EARNED, CInt(Trim([dbo_MASTER].[C_PRIORITY])) AS PRIORITY, dbo_MatrixUpt.MATRIX_ID, ([STAT1_CODE]*1) AS [STAT1 CODE], dbo_Master.STAT1_DATE, dbo_Master.DATE_DEBT, dbo_Master.PRE_J_RATE, Format([Col187],"Fixed") AS [AMT OF 1ST MORTGAGE], Format([Col189],"Fixed") AS [AMT OF 2ND MORTGAGE], dbo_Extra.MISC_CMT4, ([PRIN_COLLECTED]+[INT_COLLECTED]+[COST_RECOVERED]+[STAT_EARN]) AS PAID_TO_DATE, IIf([LPAYMNT_DATE] Is Null,"",IIf(([LPAYMNT_DATE]>[DATE_RECD] And [LPAYMNT_DATE]<Date()-181 And [PAID_TO_DATE]>0),"PMT OVER 180 DAYS",IIf(([LPAYMNT_DATE]<=Date()-91 And [LPAYMNT_DATE]>=Date()-180 And [LPAYMNT_DATE]>[DATE_RECD] And [PAID_TO_DATE]>0),"PMT 91 - 180 DAYS",IIf(([LPAYMNT_DATE]<=Date()-41 And [LPAYMNT_DATE]>=Date()-90 And [LPAYMNT_DATE]>[DATE_RECD] And [PAID_TO_DATE]>0),"PMT 41 - 90 DAYS",IIf(([LPAYMNT_DATE]>=Date()-40 And [LPAYMNT_DATE]>[DATE_RECD] And [PAID_TO_DATE]>0),"RECENT PMT"))))) AS LST_PMT_RANGE, ([PAID_TO_DATE]/[ORIG_CLAIM]) AS [%_PAID], IIf([dbo_MASTER.JMT_DATE] Is Null,IIf([DATE_DEBT] Is Not Null,CCur(((([PRE_J_RATE]/100)/365)*([BALANCE]-[COST_EXP]))*(Date()-[DATE_DEBT])+[ORIGINT]),CCur([ORIGINT])),CCur(((([POST_J_RATE]/100)/365)*[BALANCE])*(Date()-[dbo_MASTER.JMT_DATE]))) AS TOTAL_INT, ([TOTAL_INT]+[BALANCE]) AS TOTAL_DUE, StateSOL.STATUTE, IIf([LPAYMNT_DATE] Is Null,"",([LPAYMNT_DATE]+([STATUTE]*365))) AS SOL_DT
FROM (FORWARDERS INNER JOIN ((((((dbo_Debtor RIGHT JOIN dbo_Master ON dbo_Debtor.FILENO = dbo_Master.FILENO) LEFT JOIN dbo_MatrixUpt ON dbo_Master.FILENO = dbo_MatrixUpt.FILENO) LEFT JOIN dbo_Seg7 ON dbo_Master.FILENO = dbo_Seg7.PrimaryIndex) LEFT JOIN StateSOL ON dbo_Debtor.ST = StateSOL.STATE) LEFT JOIN dbo_DiaryINT ON dbo_Master.FILENO = dbo_DiaryINT.FILENO) LEFT JOIN dbo_Extra ON dbo_Master.FILENO = dbo_Extra.FILENO) ON FORWARDERS.FORW_NO = dbo_Master.FORW_NO) INNER JOIN FORWARDERS AS FORWARDERS_1 ON dbo_Master.FORW_NO = FORWARDERS_1.FORW_NO
WHERE (((dbo_Master.DATE_RECD) Between [START_DATE] And [END_DATE]) AND ((dbo_Master.SALES_NO)=[state]));