Sometimes dependent of whole configuration, like type of CPU, RAM, Chipset, etc. , for ex. Samsung CPU + 64MB RAM - no problems, your Navman S50 has very good and strong cpu samsung 2443 with 400 MHz, probably your another pna is with good configuration, at all even lower cpu + 64MB will work good, maybe not well TTS + 3d buidling + dem, but with optimization of RAM through sys.txt, it can work ok, maybe little bit more problems can be at loading bigger speedcam.txt files at 1st runing, like speedcam.txt of 3-4 MB size.