Arduino mega and rosserial problem

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I am using the arduino mega pro board https://www.sparkfun.com/products/10743

I have tested this board using stand alone sketches without ros and have no issues with that. Any sketch below 30kb works with rosserial and arduino mega pro smoothly.

As soon as my sketch size increases beyond 30kb, I start getting the error:

Unable to sync with device; possible link problem or link software version mismatch such as hydro rosserial_python with groovy Arduino

If I comment some functions in my sketch to bring the size below 30kb, things are working again.

One reason why I am using this board over arduino uno is that arduino mega lets me upload sketches over 32k (which is the maximum sketch size for arduino uno).

Any idea why this is happening? Does ros think that my mega pro board has a memory of 32k and failing when the sketch size goes beyond that.

Any help would be appreciated. Thanks.