I was having similar problem (but not the same ) And it was due to software serial pins which keep on filling the buffers of MCU.

Some times it happen that pwm pins keep on receiving data e.g. GPS also keep filling the buffer and due to that arduino freeze .

To solve this problem I open new dummy software serial port.( select any pins which is free ) and do listen to your software serial pins when you want to read it otherwise make dummy listen.

Hope it can help.

Do Innovative http://www.Innovationstracking.com

I was having similar problem (but not the same ) And it was due to software serial pins which keep on filling the buffers of MCU.

Some times it happen that pwm pins keep on receiving data e.g. GPS also keep filling the buffer and due to that arduino freeze .

To solve this problem I open new dummy software serial port.( select any pins which is free ) and do listen to your software serial pins when you want to read it otherwise make dummy listen.