P08700 error code

[shadowshlee]

HI all. I'm having a few problems with my A4 b9. It's not starting and reading error code p08700 fuel rail pressure low. In tank fuel pump and main fuel pump tested and works fine fuel filter changed,faulty injector changed ,two injector seals changed the pressure sensor has been changed and the regulator and finally the fuel rail it self has been changed. Now the fault codes are clear and not coming back on but the engine won't start and the garage are now saying they don't know what's wrong with. Has any one experienced this or have a solution? Many thanks.Ash