SUMIF function - has anyone begun receiving false results

or odd circular reference errors in the past few (2,3) days using the SUMIF
function?

I thought I just had a crashed workbook. I copied the data (edit / copy,
edit / paste special / values) to a new workbook. Column A had values 1-5,
Column K had that results I wanted to sum. In cell M2, I had the value 1,
M3 = 2, M4=3, etc. through 5. In cell N2 the formula was: =SUMIF(A:K,M2,K:K)

There were no formulas in the workbook before this. I checked. I got a
circular reference error. If I added a "1" into one of the cells in column
M, it affected the result in N2. I was able to get rid of the circular
reference error by creating the SUMIF calc in a cell around N5, N6 or
something, but then it gave me wild values.

That was Wednesday, August 13th. I thought I had a crashed workbook. Pivot
table returned the results I needed just fine. I moved on.

Today, August 14th, I opened a workbook which had been built around the
SUMIF function two weeks ago. I loaded new data in and the results which
came back were absurd. I haven't been able to get it to run again.

We've reloaded Office 2003 three times today, including two system restores
- one to last week, one to two weeks ago. No good.

My other functions, such as COUNTIF, VLOOKUP, even an ERLang B calculator
work just fine. Pivot tables are summing just fine. It appears to be this
single function, SUMIF, which has stopped working. I went to a co-workers
desk. Their results were the same. Third person thought their SUMIF
function was working (something along the lines of : =
SUMIF(A1:Q13,"<50",A1:Q13) ) However, when we changed it to whole columns,
the results went nuts. Whole numbers were used & fractionals were returned.

Anyways, I was wondering if anyone else has seen such a thing happen in the
last little while.