One of the age-old accusations against Excel is that it is error-prone.
According to research, the error rates in spreadsheets are roughly the same as in other types of activities with a similar level of complexity (such as computer programming), i.e. around 3%-5%.
The big difference is that this is recognised in software companies, whose testing processes tend to reduce this rate considerably, whereas most spreadsheet development is carried out in a much less rigorous environment.
It's not that spreadsheets are error-prone, it's that the errors aren't removed by rigorous testing.