import problems with closing date format

import problems with closing date format

I exported all the potentials to a spreadsheet from Zoho, made changes to certain fields and now on trying to import.... nothing will be accepted due to the closing date format. I did not change anything in this field! All other date fields are being accepted  as eg shown:
2014-07-25
 This is in the same format as was exported so why is there this bug?

I cannot change the format in open office to being  dd/mm/yyyy... it just stays the same when I try to format the cells?

i don't want to have to individually update each date manually. Any help please?