Hi,
This has been particulary galling and it's not the first time, either!
I had this message: "Can't change part of an array". It popped up while
dealing with some corrections to a sheet. I was left with no option but to
ctrl+alt+delete to end the task since I could not click on any part of the
sheet or other worksheets nor could I even delete the sheet or worksbook and
most functions are greyed out.

The formula was ={SUM(IF(Purchases!$F$2:$F$5000="Goldman
Sachs",IF(Purchases!$D$2:$D$5000=DATEVALUE("29/04/2004"),Purchases!$I$2:$I$5000,0),0))}.

Since I discovered that this actually replicated the cell above and should
have been analysing purchases via Investec, not Goldman Sachs, I changed the
formula to read Investec. This is one of 25 different brokers in a list where
each one analyses the purchases using the above formula.
The system baulked at the first change and so I deleted the whole formula to
re-write it, then the notice popped up.
Q1: If this notice pops up again, is there any way to back out of it
without losing everything?
Q2: What causes this notice to pop up? If I understand that, I can avoid
the cause.

Many thanks
Geoff