Manipulating section checkbox

Hi,

I want to enable a section checkbox when there exists a certain file within the $EXEDIR directory. I already have:

!define MUI_CUSTOMFUNCTION_GUIINIT myGuiInit

Function myGuiInit
IfFileExists "$EXEDIR\win32\mysql-4.0.18-win\SETUP.EXE" mysql_found mysql_done
mysql_found:
MessageBox MB_OK "enable checkbox"
goto mysql_done
mysql_done:
FunctionEnd

Instead of the MessageBox I would like to enable an RO section again. How can this be done?

Use the macros in Sections.nsh. See one-section.nsi as an example.