Recently we have received reports that the MMC and SD cards, even though they appear to mount and work, will malfunction in the device after a while, resulting in loss of data.
The error has been tracked to the root directory. When there were more than a certain number of files on the card, it malfunctioned. That is why it didn't appear until the card was used for a while. The firmware has now been fixed, but additionally it is a good idea to reformat the card from time to time.
2011-08-19: Memory Cards
2011-08-11: Bottom Level Determination (software update 2.3.2)
2010-07-22: Measuring Turbidity: New Revelations
2010-07-21: Exporting Turbidity Data (software update 2.2)
Disclaimer - This information is given in good faith but without any warranty regarding the applicability for any specific situation. For consulting see Services.