C# - Calling Function Referenced By Project

As per [URL] How can I achieve this? 'processPacketVB' is a 'variable' but is used like a 'method' is the error I'm getting with these references to the project and class and function.

using VBProcessPacket;
namespace UIST {
public partial class FormActionMenu : Form {
private void timerDelay_Tick(object sender, EventArgs e) {
VBProcessPacket.ProcessRX processPacketVB = new VBProcessPacket.ProcessRX();
//read the receive buffer as a string
RXpacket = processPacketVB("test"); // processPacketVB throws the error 'processPacketVB' is a 'variable' but is used like a 'method'