Just to be sure; are there any SPI devices connected to the Waspmote?
It sounds like the SPI databus is unreliable and when I faced problems with my SD card operations I had to manually pull DIGITAL pins which controlled other devices high to make sure the SPI data is only being used by the SD card.
I don't use a Wasp P&S but am developing with just a Waspmote and some SPI peripherals on DIGITAL 4,7 and 8.
Running the SD examples all returned errors (or performed really poor at best), but when manually setting DIGITAL 4,7, and 8 to OUTPUT and then pulling them HIGH made the examples run without any problems.
Hope this may help you a little further in solving your issue.
I didn't find the right solution from the internet.
Data Analysis Example