Engine errror

I hope not to break the rules of this forum, but I want to ask the opinions of the community.

I recently bought a Skoda Fabia Combi 1.2 12V in 2003 and went out with her 1800 km without any problems.

After that came on board with the yellow bulb that one geared motor (engine).

I went to someone who has test equipment and following error occurred:

1. catalyst I

2. EGR

3. a spark working or not

4. and one more error

Reset the four errors and tester visible only the first two (see that are reset) and disappeared the error from board .

After exactly 300 km throughout the city (3000-35000 rpm) error reappeared.

I test again and the two errors have reappeared (1th and 2nd).

Have been reset and the two service errors. it was bad gassoline? .

But more than other 300 km and the problem reappeared.

What to believe?.

Does anyone know what is the solution?