Hi and welcome to the forum, Toni!
The available speeds are 2.4x, 4x, 6x. The ones supported by the writer). For the 1x I guess it uses a generic write approach. Might try one of those speeds.
Tried to find an updated firmware for that writer (A Dell?) but no luck.
You might get better luck with Verbatim 2.4x rated discs (Made in Singapore) as the ones you use can be tricky in older writers.
Focus Servo Error might indicate a faulty writer, but I guess you doesn't have any issues burning other branded discs?