VSTO Write Dictionary To Range Extension Method
You have a lot of unnecessary vertical spacing which should be removed to improve readability.  



Based on the naming guidelines input parameter should be named using camelCase casing.  



Because WriteToRange() can be called also as a normal static method you need to check both input parameters for null.  



The storeDictionaryData is basically a object[columns, rows] this should be reflected by the counter variables. You can just rename them valueCounter -&gt; column, keyCounter -&gt; row.  



You don't need the checks keyCounter &lt; storeDictionaryData.GetLength(1) and valueCounter &lt; storeDictionaryData.GetLength(0) because at the point where you create the array you have taken care of the upper bounds of both dimensions. Both conditions won't evaluate to false.  



toRange is poorly named. Consider to name it destinationRange or simply destination. Then a good pattern would be also to rename DictToRange to source. 



You should allow your variables to breathe by adding spaces between variables and operators.  



Taking the above points into account we can refactor the method to  

public static void WriteToRange(this Dictionary&lt;string, object[]&gt; source, excel.Range destination)
{
   if (source == null) { throw new ArgumentNullException("source"); }
   if (destination == null) { throw new ArgumentNullException("destination"); }
   if (source.Count == 0) { throw new ArgumentOutOfRangeException("source"); }

   object[,] storeDictionaryData = new object[source.Max(maxValues =&gt; maxValues.Value.Length), source.Count];

   int column = 0;
   int row = 0;

   foreach (var key in source.Keys)
   {
       foreach (var value in source[key])
       {
           storeDictionaryData[column, row] = value;
           column++;
       }

       row++;
       column = 0;
   }

   dynamic rangeToFill = destination.get_Resize(storeDictionaryData.GetLength(0), storeDictionaryData.GetLength(1));
   rangeToFill.Value = storeDictionaryData;
}