sorry. i'm not getting a 500, it does return ok. if i pass 5, it dumps var0-4, which is fine. if i pass more than 5, it appears to call the script again for each multiple of 5:

$VAR1 = '6'; $VAR2 = undef; $VAR3 = '11'; $VAR4 = undef; $VAR5 = '3'; 
+$VAR6 = undef; $VAR7 = '7'; $VAR8 = undef; $VAR9 = '9'; $VAR10 = unde
+f; $VAR11 = '2'; $VAR12 = undef; $VAR13 = '12'; $VAR14 = undef; $VAR1
+5 = '8'; $VAR16 = undef; $VAR17 = '4'; $VAR18 = undef; $VAR19 = '1'; 
+$VAR20 = undef; $VAR21 = '0'; $VAR22 = undef; $VAR23 = '10'; $VAR24 =
+ undef; $VAR25 = '13'; $VAR26 = undef; $VAR27 = '5'; $VAR28 = undef; 
+Content-type: text/html $VAR1 = '6'; $VAR2 = undef; $VAR3 = '11'; $VA
+R4 = undef; $VAR5 = '3'; $VAR6 = undef; $VAR7 = '7'; $VAR8 = undef; $
+VAR9 = '9'; $VAR10 = undef; $VAR11 = '2'; $VAR12 = undef; $VAR13 = '1
+2'; $VAR14 = undef; $VAR15 = '8'; $VAR16 = undef; $VAR17 = '4'; $VAR1
+8 = undef; $VAR19 = '1'; $VAR20 = undef; $VAR21 = '0'; $VAR22 = undef
+; $VAR23 = '10'; $VAR24 = undef; $VAR25 = '13'; $VAR26 = undef; $VAR2
+7 = '5'; $VAR28 = undef; Content-type: text/html 
 <etc, there's a lot more>

Software error:

timeout
[download]

i can't see a possible reason for the extra "Content-type". the actual error appears to be either the main process or the children not dying when their time is up.