improve compatibility with php 5.3

Hello,
after having migrate my website from a shared hosting with php 5.2 to a vps with php 5.3, I have problem with ni_cron.
In fact, looking at the log messages when cron starts, I have this:
4366894 28/Set 14:36 error php md5_file() [function.md5-file]: Filename
cannot be empty in
/var/www/vhosts/spazioausili.net/httpdocs/s
ites/all/modules/ni_cron/ni_cron.module on
line 55.

I don't know if it depends on my configuration, anyway it seems strange to me.
Any ideas?