What cause reflector to raise exception on this IL

[ExeLord]

I have target which is obfuscated and all strings are encrypted with simple encryption routine, here is string decryption function:

.method privatescope hidebysig static string ᐁ(string) cil managed
{
    .maxstack 4
    .locals init (
        [0] char[] chArray,
        [1] int32 num)
    L_0000: ldarg.0 
    L_0001: call instance char[] [mscorlib]System.String::ToCharArray()
    L_0006: dup 
    L_0007: stloc.0 
    L_0008: dup 
    L_0009: ldlen 
    L_000a: conv.i4 
    L_000b: dup 
    L_000c: ldc.i4.0 
    L_000d: bgt.s L_001b
    L_000f: pop 
    L_0010: newobj instance void [mscorlib]System.String::.ctor(char[])
    L_0015: call string [mscorlib]System.String::Intern(string)
    L_001a: ret 
    L_001b: ldc.i4.m1 
    L_001c: add 
    L_001d: dup 
    L_001e: stloc.1 
    L_001f: ldloc.0 
    L_0020: ldloc.1 
    L_0021: ldelem.u2 
    L_0022: ldc.i4 0x1469
    L_0027: sub 
    L_0028: conv.u2 
    L_0029: stelem.i2 
    L_002a: ldloc.0 
    L_002b: ldloc.1 
    L_002c: br.s L_000b
}

when I try to decompile it with reflector, it will raise an exception, here is reflector exception info:

Translation failure in 'ᐁ.ᐁ(String) : String' in 'Telligent.Registration, Version=5.0.40702.0, Culture=neutral, PublicKeyToken=null'.

System.InvalidOperationException

InnerException:

Expression stack is empty at offset 001D.

System.InvalidOperationException

   at ឺ.ᜀ()
   at ឺ.ᜀ(BinaryOperator A_0)
   at ឺ.᜘()
   at ឺ.ᜊ(Int32 A_0)
   at ឺ.ᜋ(Int32 A_0)
   at ឺ.ᜂ(Int32 A_0, Int32 A_1)
   at ឺ.ᜀ(IMethodDeclaration A_0, IMethodBody A_1)
   at ឤ.ᜀ(IMethodDeclaration A_0)
   at ឥ.ᜁ(IMethodDeclaration A_0)
   at ᝎ.ᜀ(Boolean A_0, Boolean A_1, Boolean A_2)

.NET Reflector 5.1.6.0
.NET Framework 2.0.50727.3074
Microsoft Windows NT 6.0.6001 Service Pack 1
Culture: en-US (en-US)

why it cause reflector decompiler to raise exception ?

I can send target assemlby if needed.

[Kurapica]

this exception is usually raised when the control-flow of the code is obfuscated.