can not do rm on a file

[Tapas Mishra]

This is the most frustrating problem I have ever faced and posting here.
I have a file file.something ls -l output

-rwxr-xr-x 1 tapas tapas        30 2010-10-06 20:14 file1.txt
-rwxr-xr-x 1 tapas tapas 441712640 2011-01-08 02:40 file2.exe

now I do as root

rm file2.exe
rm: cannot remove `file2.exe': Read-only file system

How is this possible inspite of the read write permissions I am not
able to delete it I have tried it doing as root even.
The OS is 10.04 64 bit.


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