"When i'm using 16MHz internal frequency (OSCCON = 01111000) everthing works fine."

You thought everything worked fine.

I see no DEFINE OSC 16 or 32.

"My programm does software-pwm, lighting 5 LED's up and down."

May I suggest that you use DT's MIBAM for these 5-LEDS ?
With 32Mhz, you can get high refresh rate with MIBAM.