Task: Straddling checkerboard
C#: using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace StraddlingCheckerboard
{
    class Program
    {
        public readonly static IReadOnlyDictionary<char, string> val2Key;
        public readonly static IReadOnlyDictionary<string, char> key2Val;

        static Program()
        {
            val2Key = new Dictionary<char, string> {
                {'A',"30"},  {'B',"31"}, {'C',"32"},  {'D',"33"},  {'E',"5"},   {'F',"34"},  {'G',"35"},
                {'H',"0"},   {'I',"36"}, {'J',"37"},  {'K',"38"},  {'L',"2"},   {'M',"4"},   {'.',"78"},
                {'N',"39"},  {'/',"79"}, {'O',"1"},   {'0',"790"}, {'P',"70"},  {'1',"791"}, {'Q',"71"},
                {'2',"792"}, {'R',"8"},  {'3',"793"}, {'S',"6"},   {'4',"794"}, {'T',"9"},   {'5',"795"},
                {'U',"72"},  {'6',"796"},{'V',"73"},  {'7',"797"}, {'W',"74"},  {'8',"798"}, {'X',"75"},
                {'9',"799"}, {'Y',"76"}, {'Z',"77"}};

            key2Val = val2Key.ToDictionary(kv => kv.Value, kv => kv.Key);
        }

        public static string Encode(string s)
        {
            return string.Concat(s.ToUpper().ToCharArray()
                .Where(c => val2Key.ContainsKey(c)).Select(c => val2Key[c]));
        }

        public static string Decode(string s)
        {
            return string.Concat(Regex.Matches(s, "79.|7.|3.|.").Cast<Match>()
                .Where(m => key2Val.ContainsKey(m.Value)).Select(m => key2Val[m.Value]));
        }

        static void Main(string[] args)
        {
            var enc = Encode("One night-it was on the twentieth of March, 1888-I was returning");
            Console.WriteLine(enc);
            Console.WriteLine(Decode(enc));

            Console.ReadLine();
        }
    }
}

VB: 

Function encrypt(ByVal originalText, ByVal alphabet, blank1, blank2)
  Const notEscape = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ."
  Dim i, j, curChar, escChar, outText
  Dim cipher  
  Set cipher = CreateObject("Scripting.Dictionary")
  
  alphabet = UCase(alphabet) : j = 0
  For i = 1 To 28
    curChar = Mid(alphabet, i, 1)
    Select Case True
      Case i>= 1 And i<= 8
        If j = blank1 Or j = blank2 Then j = j + 1  
		cipher.Add curChar, CStr(j)
        j = j + 1
      Case i>= 9 And i<=18
		cipher.Add curChar, CStr(blank1) & CStr(i -  9)
      Case i>=19 And i<=28
		cipher.Add curChar, CStr(blank2) & CStr(i - 19)
    End Select 
    If InStr(notEscape, curChar) = 0 Then
      escChar = curChar
      
    End If
  Next 
  For i = 0 To 9: cipher.Add CStr(i), cipher(escChar) & CStr(i): Next 
  
  originalText = UCase(originalText)
  For i = 1 To Len(originalText)
    outText = outText & cipher(Mid(originalText, i, 1))
  Next 
  encrypt=outText
End Function 
 
Function decrypt(ByVal cipherText, ByVal alphabet, blank1, blank2)
  Const notEscape = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ."
  Dim i, j, curChar, escCipher, outText
  Dim cipher  
  Set cipher = CreateObject("Scripting.Dictionary")
  
  alphabet = UCase(alphabet) : j = 0
  For i = 1 To 28
    curChar = Mid(alphabet, i, 1)
    Select Case True
      Case i>= 1 And i<= 8
        If j = blank1 Or j = blank2 Then j = j + 1  
		cipher.Add CStr(j),curChar
        j = j + 1
      Case i>= 9 And i<=18
        cipher.Add CStr(blank1) & CStr(i -  9), curChar
      Case i>=19 And i<=28
        cipher.Add CStr(blank2) & CStr(i - 19), curChar
    End Select 
    If InStr(notEscape, curChar) = 0 Then
      
      arrayKeys=cipher.keys
      escCipher = arrayKeys(cipher.count-1)
      
    End If
  Next 
  For i = 0 To 9: cipher.Add escCipher & CStr(i), CStr(i): Next 
  
  i = 1
  Do While i <= Len(cipherText)
    curChar = Mid(cipherText, i, 1)
    If curChar = CStr(blank1) Or curChar = CStr(blank2) Then
      curChar = Mid(cipherText, i, 2)
      If curChar = escCipher Then curChar = Mid(cipherText, i, 3)
    End If 
    outText = outText & cipher(curChar)
    i = i + Len(curChar)
  Loop 
  decrypt=outText
End Function 
 
  message = "One night-it was on the twentieth of March, 1888-I was returning"
  cipher = "HOLMESRTABCDFGIJKNPQUVWXYZ./"
  
  
  
  
  Buffer=Buffer & "Original: " & message & vbCrlf 
  encoded = encrypt(message, cipher, 3, 7)
  Buffer=Buffer &  "encoded: " & encoded & vbCrlf
  decoded = decrypt(encoded, cipher, 3, 7)
  Buffer=Buffer &  "decoded: " & decoded & vbCrlf
  Wscript.Echo Buffer