[Gnuplot-info] wrong prompt while using 'update' command after 'fit'

[boluor <bo...@si...>]

i first define a function : f(x) = a *x**2 + b *x + c;

then : fit f(x) 'data' via a,b,c;

then i want to store the a,b,c to a file names 'a.log'.

so i typed : update 'a.log'

but i got the wrong prompt : 

  gnuplot> update 'a.log'
         Could not rename file a.log to a.log.old

i want to know why??

i use gnuplot Version 4.2 patchlevel 5 , under ubuntu linux9.10.

thank u all.