Odd error.

I have a problem with my procmail setup, which only occurs sometimes, ie
lots of times it works fine.

Well here's the recipe I have problem with:
======================================================================
:0B
* 1^1 ^(.|$)
{
        VAR8 = $=
}
VAR9 =  `/usr/local/bin/formail -zx from:`
VAR10 =  `/usr/local/bin/formail -zx subject:`

:0c:lock
|echo $VAR8 lines, `/usr/local/gnu/bin/date +%e`/`/usr/local/gnu/bin/date 
+%m`/`/usr/local/gnu/bin/date +%y`, `/usr/local/gnu/bin/date 
+%k`:`/usr/local/gnu/bin/date +%M`, $VAR9, $VAR10 | gzip >> log.gz
======================================================================

Please do not commment the layout, it is generated automaticly.
It works fine most of the time, but once in a while I get the following
message:

======================================================================
procmail: Error while writing to "echo $VAR8 lines, `/usr/local/gnu/bin/date 
+%e`/`/usr/local/gnu/bin/date +%m`/`/usr/local/gnu/bin/date +%y`, 
`/usr/local/gnu/bin/date +%k`:`/usr/local/gnu/bin/date +%M`, $VAR9, $VAR10 | 
gzip >> log.gz"
======================================================================

Here's the content of the variables, as procmail report it:
procmail: Assigning "VAR8=102"
procmail: Assigning "VAR9=Operator <root(_at_)imada(_dot_)ou(_dot_)dk>"
procmail: Assigning "VAR10=Output from "cron" command"

Thanks in advance and kind Regards Jesper.