Older decompilers usually only work on EX4 files compiled with MT4 builds prior to 600 .
To understand why a decompiler is used, it is essential to know the difference between the two primary file types in MetaTrader 4: ex4tomq4decompiler404011 225
If you are looking for a legitimate way to recover lost source code for your own EA or indicator, consider: Older decompilers usually only work on EX4 files