If you have received logs normally and then they stop suddenly, then one of these could be the cause:

• There have been no activities to report.
• The phone is turned off or roaming.
• The phone is outside of an area with GPRS or Wi-fi internet access is available.
• The software was discovered and removed by the end-user.
  

Once the phone is turned on or comes back in range it will start uploading logs again starting where it left off. In most cases, if your logs stop yet none of the above apply, then just rebooting the phone will clear the memory and allow the program to function normally again.