P2293 Low Fuel Pressure Diagnostic

I recently had my 2006 Audi A4 2.0T Serviced for the diagnostic of P2293 which indicates Low Fuel Pressure. At first hoping it was a sensor on the fuel pump it was realized the camshaft as well as the high pressure fuel pump had to be replaced. Although the cost of parts was not that extreme, the labor was intensive and costed a pretty penny. Nearly a day after I got the car back and drove it, the check engine light came back on. Does anyone know what the problem could be now? All parts were brand new when installed, and all fluids were changed as well after the service.  

In the end the fourth lifter had failed on the new Camshaft. Parts were replaced by the shop at no cost.