Dear Mario,
   I traced the IL code, and found some problems in the following code, I
don't know if it is a bug.
In this method , it first stored the count of the socketlist we passed in
with out any range check,
and then if the count isn't zero, the  method will always allocate a native
int[64] array,
which ofcourse doesn't match with the value in FileDescriptorSet.Count,
then the IndexOutOfRangeException is thrown in the following codes.

maybe the conceptual code in c# like this:

FileDescriptorSet(Int32 count) {
   Count = count;
   if (!Count)
       Array = new IntPtr(64);
   else Array = null;
}

any comments are welcome.

regards,

Jonny Yu

System.Net.Sockets.FileDescriptorSet
.method public hidebysig specialname rtspecialname
       instance void  .ctor(int32 count) cil managed
{
 // Code size       27 (0x1b)
 .maxstack  8
 IL_0000:  ldarg.0
 IL_0001:  ldarg.1
 IL_0002:  stfld      int32 System.Net.Sockets.FileDescriptorSet::Count
 IL_0007:  ldarg.0
 IL_0008:  ldarg.1
 IL_0009:  brfalse.s  IL_0014
 IL_000b:  ldc.i4.s   64
 IL_000d:  newarr     [mscorlib]System.IntPtr
 IL_0012:  br.s       IL_0015
 IL_0014:  ldnull
 IL_0015:  stfld      native int[]
System.Net.Sockets.FileDescriptorSet::Array
 IL_001a:  ret
} // end of method FileDescriptorSet::.ctor