It cannot decompile files created with MT4 Build 600 or higher . Modern builds use a different compilation method that produces binary code rather than the byte code this tool was built to handle.
MetaQuotes has consistently updated the MT4 compiler, introducing new opcodes and obfuscation techniques. Previous decompilers often crashed or produced garbage code when faced with builds beyond 1170. Version 4.0.432 claims compatibility up to MT4 build 1400. Ex4 To Mq4 Decompiler 4.0.432 - Updated