There doesn't appear to be anything wrong in the code you showed, so it's probably memory corruption or some similar problem (arrays too small, etc). Test your code out on a PC; if you have a specific (complete) piece of code that works fine on a PC but doesn't work on the PSP then maybe someone here can point out a problem.
@Crux
Shouldn't your output contain the words "noteTime:" and "noteButton:"? Did it really print 3 digits after the decimal point (0.000), even though you specified 1 digit?
Anyway, if atof conversion fails it returns 0.0. Thus I would check the input strings and make sure there are no funny/unexpected chars.