read / write userblock error : no valid system id block

i have the following problem:
after x times writing or reading my userblock succesfull i get
the return error -2
i don’t understand why i get this after i could do this x times
also this problem occured after i addjusted my app to read an ibutton
but this is mearly reading/writing to a serial port with some delays
i dont even user the read/write userblock during my communication with the ibutton yet i get the error after i read from the ibutton.

this error probably causes my app to hang on any read or write userblock that follows.
can somebody help me on this or have any tips on good use of read/write userblock

here is some info of my board when i run userblockinfo.c:
System ID Block version: 4

Contains mirrored ID/User blocks, which ensures that there is
always a correct version of User block information written.

Combined ID and User blocks consume 0x00008000 (32768)
bytes at the top of the first flash.

Combined ID plus User blocks size: 0x00004000 (16384).

System ID block size: 0x00000084 (132).
User block size: 0x00003F7C (16252).
Available User block size: 0x00003F7C (16252).
Reserved User block size: 0x00000000 (0).

the size of my variable to write in the userblock = 12157
plz respond if you know anything, its urgent
grz muk