PNAs are known to have a lot of problems with their internal flash memory.

No matter if you are using the internall flash, or an external SD card, you should be very careful about the following issues:

• Do NOT connect your PNA to the PC using ActiveSync.
  
• Do NOT extract the SD while the software is running, even if you have switched off the PNA or PDA
• Do NOT reset the PNA/PDA while LK is running

Repeat this to yourself, as a mantra: " I will not switch off the PNA while LK still running, because it may run out of battery and thus reset. If it resets while LK is running, I will loose data, the flash will be corrupted, I may experience crashes anytime during a flight. This is why I won't switch off the PNA while LK is still.. " .. etc.etc.

Follow this simple advise, and you won't experience crashes.