Failed Checksum increasing a lot

I am using a Grove GPS and have a failedChrecksum() counter that tells me how many sentences have failed the checksum test. Problem is, the counter is increasing about every second output, with seven satellites visible. I only have one delay() in my code.
Is this normal, or am I doing something wrong?
Thanks in advance.

Can you provide me with more information about failedChrecksum(), for example, where did you see this function?