Could be a few things. If it has a fuel filter with only 2 pipes and an electrical sensor it is most likely the fuel filter needs changing. But if they flash and the enging stops it is something more serious. One point here though, before you take it to get the diagnostic code read, make sure the fault warning light is on. Normally the fault has to occur twice before it will lock in an error code!
Hi, should not be a problem if you keep them on the same axle, BTW it is illegal to mix them anyway! It is better that you have the 225's on the front, 225 is the effective width of the tyre and will obviously give more grip that the 205. The other bit 55/50 is the profile.