sysstat sar - is not working suddenly!

[SupermanInNY]

here is a weired situation.

I log in as username
then I do su - to go to root

If I type sar as ROOT, I get the following error:

:/root # sar
Invalid system activity file: /var/log/sa/sa06 (0)


If I do an Exit,. and go back to username and type sar I get the following:

[username@host ~]$ sar
Linux 2.6.9-55.0.9.ELsmp (host.server.info) 10/06/2007

05:57:02 AM CPU %user %nice %system %iowait %idle
06:00:01 AM all 1.55 0.00 0.16 0.56 97.74
06:10:01 AM all 2.41 0.00 0.39 0.96 96.24
06:20:01 AM all 2.15 0.00 0.66 12.14 85.05
06:30:01 AM all 3.16 0.00 0.88 13.28 82.68
Average: all 2.48 0.00 0.60 8.05 88.87
[username@host ~]$


or

[alon@host ~]$ sar -q
Linux 2.6.9-55.0.9.ELsmp (host.server.info) 10/06/2007

05:57:02 AM runq-sz plist-sz ldavg-1 ldavg-5 ldavg-15
06:00:01 AM 5 142 0.07 0.07 0.07
06:10:01 AM 7 141 0.06 0.06 0.05
06:20:01 AM 3 141 1.05 0.44 0.18
06:30:01 AM 6 142 0.08 0.23 0.22
Average: 5 142 0.32 0.20 0.13
[alon@host ~]

How weired is that?

It seems that root is having problems reading whereas username doesn't have a problem.

I can't figure this out!

Any pointers?

-Alon.