Problem with Backups through mysqldump

[#1]

I have a problem with the database backup process we have been running for some years.
The process uses the system command from within php to run mysqldump and output to a file.
This is run through a web page (under security) at a time of our chosing, we then copy the file and it is deleted from the PlusNet server.
The process has been running fine for years.
Since the new platform, the process creates a file of zero bytes rather than the sqldump we would expect.
I have played with this for hours trying to ascertain whether the problem is with new php version or, somehow, with file permissions.
We are writing the file to a directory which has no other files and the permissions appear to be 750 for the directory and 644 for the created (but empty) file.
Anyone come accross this?

[#2]

Have just picked up your ticket, it will be looked into shortly, might not be until tomorrow though (ref: 300397).
Edit: mysqldump now installed

[#3]

Now works as expected.  Delighted it was not a permissions issue!
Thanks Bob