triangle in upper left corner of a cell

[knowtrump]

I hope I am not being repetitive. I tried to post this question earlier, but it didn't show up. I apologize ahead of time also, I think I ought to kow the answer. A little more detail this time.
I try to manage my check book using excel. Column A is Date, Column B, is the Ck recipient and ck #, in column C I enter and x, in column D I enter either cc or ck, Columns e through k are amounts taken from various fund designations, column L sums column e through k, in column M I enter the formula =if(and(c(row number)=x,or(d(row number)=cc,d(row number)=ck)),L(row number),"") e.g.,=if(and(C1=x,or(D1=ck,D1=cc)),L1,"") When my bank statement arrives I remove the x in column c. That leaves a list of the checks still outstanding in column M.
For some reason the "D"(row number in the formula is being changed to "B" row number. When I try to correct it i get the triangle in the upper corner of the cell and the formula does not work.
Man that is a lengthy way of asking," what does the triangle mean and what causes it?"

[NBVC]

See here:

http://www.excelforum.com/showthread.php?t=647253