Cycle + Cancel button = does not work

[and84]

Hello All.
Faced with the problem.
In the script uses the cycle of reading data from a file:

PHP Code:

........
!define MUI_PAGE_CUSTOMFUNCTION_SHOW cancel_ON

Section ""
StrCpy $2 "0"
next:
        IntOp $2 $2 + 1
        ReadINIStr $R1 '$EXEDIR\data.ini' 'FILE $2' 'NAME'
        ReadINIStr $R2 '$EXEDIR\data.ini' 'FILE $2' 'PATH'
        ReadINIStr $R5 '$EXEDIR\data.ini' 'FILE $2' 'URL'
        ReadINIStr $R3 '$EXEDIR\data.ini' 'FILE $2' 'CRC'
        ReadINIStr $R4 '$EXEDIR\data.ini' 'FILE $2' 'END'
        StrCmp $R4 "END" next 
        DetailPrint "OK"      
quit:
SectionEND

Function cancel_ON
         GetDlgItem $R0 $HWNDPARENT 2 
         EnableWindow $R0 1 
FunctionEnd 


As a result ...
Clicking on the Cancel button, it does not work the first time (have to press several times)

What problem?