This error seems to occur on all user stats.
Credits in "last month" are shown as ZERO when credits are in "last week".
This is easily seen by looking at:

SETI@home user stats
User stats
Users 80001 - 80100
Sorted on accumulated credit last month (reversed)
Total number of users: 169125

There was a post about monthly stats being a month "out of synch".
Maybe it is associated with that problem?

Keith