pl help me in oracle

hi,
 ls_line1 :=SUBSTR(trim(ls_line1),6,LENGTH(ls_line1));
// this variable contains the value '126/1'
 ls_statement_no := SUBSTR(ls_line1, 1,INSTR(ls_line1,'/',1)- 1 ) ;
// this variable contains the value '126'
li_statement_no:=to_number(ls_statement_no);

// it is working fine

 ls_page_no := SUBSTR(trim(ls_line1),
INSTR(ls_line1,'/',1)+1,LENGTH(ls_line1));
// this variable contains the value '1'

li_page_no:=to_number(ls_page_no)
when we convert the string to number , i got an error. the error is 06502- character to number conversion error even if i did the implicit conversion, it is throwing an error Received on Thu Sep 28 2006 - 02:44:57 CDT