unexpected flash erasing MSP430

Hi to all.
 i'm using the flash programming in my project: from time to time
 device adds some data to info memory. The algorithm of read/write
 operation with segments is according to datasheet slau056e.pdf.
 All devices were verifying out and there were no troubles with them.
 But after a time some devices(for about 30) had fallen out.
 Examination had shown that instead of the data there is just 0xff in
 the flash(info memory). this problem occurs oftenly enough.
 Supervisor is on therefore i'm not sure that supply causes it. During
 all my experiments with the supply voltage not once error had
 occured. Actually it seems very hard to initiate this error in all
 the way.
 besides supervisor, it was decided to use other hints in a project to
 escape unexpected flash erasing. Each segment is written twice,
 algorithm uses CRC to check the storing data that must be written,
 each segment can be written only after the previous will be veryfied.
 After all, the number of cases with errors was appreciably decreased,
 but the problem isn't solved.

 I'm using msp430f413.
 surfing the blogs i saw that this problem is widespread. but i didn't
 find no solving
 
 Can anybody help me?