Error 1 An object reference is required for the non-static field, method, or property

Error 1 An object reference is required for the non-static field, method, or property 'ConsoleApplication_FileTest.Program.GetAverageSalary(string)' C:\Users\Dawn\documents\visual studio 11\Projects\ConsoleApplication_FileTest\ConsoleApplication_FileTest\Program.cs 98 24 ConsoleApplication_FileTest
static void Main(string[] args)
{

Dictionary<string, double> averages = new Dictionary<string, double>();
string filename = "c:\\test.txt";
averages = GetAverageSalary(filename)
}

=====================
Dictionary<string, double> GetAverageSalary(string filename)
{
...

The Main() method is static, GetAverageSalary() is not, so it can't be called without an object.
Just add "static" in front of the declaration of GetAverageSalary() - just like the one Main() already present in front of Main().