The "os" module is not included in LuaRT. To use it for a compiled executable, you will need to compile your script with the dynamic runtime, and use the the std version of Lua54.dll file along the generated exe.
LuaRT Studio uses the std lua54.dll. You can find it in the bin\ folder.
With LuaRT you can find it in bin\std folder.
As a side note, instead of
os.execute() you can use
sys.cmd() with LuaRT