Command: de4dot.exe -f "D:\xxks\EXAMTEACHER.exe" -o "D:\xxks\EXAMTEACHER_de4dot.exe"
Output:

de4dot v3.1.41592.3405 Copyright (C) 2011-2014 [email protected]
Latest version and source code: https://github.com/0xd4d/de4dot
21 deobfuscator modules loaded!

Detected Dotfuscator 12345:1:2:4.2.5000.27554 (D:\xxks\EXAMTEACHER.exe)
Cleaning D:\xxks\EXAMTEACHER.exe
WARNING: Could not deobfuscate method 06000185. Hello, E.T.: System.ApplicationException
Renaming all obfuscated symbols
Saving D:\xxks\EXAMTEACHER_de4dot.exe
ERROR: Error calculating max stack value. If the method's obfuscated, set CilBody.KeepOldMaxStack or MetaDataOptions.Flags (KeepOldMaxStack, global option) to ignore this error. Otherwise fix your generated CIL code so it conforms to the ECMA standard.
ERROR: Instruction operand is null
ERROR: Operand is not a local/arg
ERROR: Instruction is null
ERROR: Target instruction is too far away for a short branch. Use the long branch or call CilBody.SimplifyBranches() and CilBody.OptimizeBranches()
Ignored 7741 warnings/errors
Use -v/-vv option or set environment variable SHOWALLMESSAGES=1 to see all messages

Why?