Please describe the problem:
Correct formula:
=if(count(P$3:Y$3)<count(P11:Y11),"Warn!",if(sumif(P11:Y11,">0")>0,(if(or(countif(P11,"A")>0,count(P$3)=0),0,P11/P$5*P$3)+if(or(countif(Q11,"A")>0,count(Q$3)=0),0,Q11/Q$5*Q$3)+if(or(countif(R11,"A")>0,count(R$3)=0),0,R11/R$5*R$3)+if(or(countif(S11,"A")>0,count(S$3)=0),0,S11/S$5*S$3)+if(or(countif(T11,"A")>0,count(T$3)=0),0,T11/T$5*T$3)+if(or(countif(U11,"A")>0,count(U$3)=0),0,U11/U$5*U$3)+if(or(countif(V11,"A")>0,count(V$3)=0),0,V11/V$5*V$3)+if(or(countif(W11,"A")>0,count(W$3)=0),0,W11/W$5*W$3)+if(or(countif(X11,"A")>0,count(X$3)=0),0,X11/X$5*X$3)+if(or(countif(Y11,"A")>0,count(Y$3)=0),0,Y11/Y$5*Y$3))/sum(AB11),0))

Get corrupted to:
=if(count(P$3:Y$3)<count(P11:Y11),"Warn!",if(sumif(P11:Y11,">0",)>0,(if(or(countif(P11,"A")>0,count(P$3)=0),0,P11/P$5*P$3)+if(or(countif(Q11,"A")>0,count(Q$3)=0),0,Q11/Q$5*Q$3)+if(or(countif(R11,"A")>0,count(R$3)=0),0,R11/R$5*R$3)+if(or(countif(S11,"A")>0,count(S$3)=0),0,S11/S$5*S$3)+if(or(countif(T11,"A")>0,count(T$3)=0),0,T11/T$5*T$3)+if(or(countif(U11,"A")>0,count(U$3)=0),0,U11/U$5*U$3)+if(or(countif(V11,"A")>0,count(V$3)=0),0,V11/V$5*V$3)+if(or(countif(W11,"A")>0,count(W$3)=0),0,W11/W$5*W$3)+if(or(countif(X11,"A")>0,count(X$3)=0),0,X11/X$5*X$3)+if(or(countif(Y11,"A")>0,count(Y$3)=0),0,Y11/Y$5*Y$3))/sum(AB11),0))
i.e. the extra comma is here ..................................^^



Steps to reproduce:
1. within the spreadsheet, initiate a recalculation of the formula
2. 
3. 


Actual results:
the extra comma appears, and a #VALUE or other error occurs

Expected results:
The formula to remain unchanged and a newly calculated value to appear.

Does this happen every time?
Yes.

Other information:
I would like to send a sample version of the spreadsheet, so it is the problem
could easily be re-created and investigated. May be you could email and I will
forward a sample of the spreadsheet?