LinuxQuestions.org - -bash: /dev/null: Permission denied and growing size

hi guys

I gotta a Centos 5.0 that suddenly every time I log in I get this

Code:

-bash: /dev/null: Permission denied

-bash: /dev/null: Permission denied

-bash: /dev/null: Permission denied

.....

I check the system and

Code:

ls -lh /dev/null

-rw-r--r-- 1 root root 7.8M Jun 11 12:51 /dev/null

and If check a system running OK the permissions and file type are different

Code:

ls -lh /dev/null

crw-rw-rw- 1 root root 1, 3 May  9 00:57 /dev/null

1. what could be the reason that caused this null file change the permissions and file type?
also notice the last modification time is equal to my date and the file is 7MB????

2. How can I get it back to its original file type? for permissions would be chmod 644 but for file type? or Can I copy the file from another server working fine?

thanks a lot