Why do I get an error message when adding cash account feature?

Cash account in investment details allows the user to add cash in three different ways; default setting determined by the provider, pound amount added by the user or % amount of the total investment. If you have selected to add a pound amount, check that the total investment amount is not less than the amount in the cash account. 

Both the pound amount and the percentage of the investment come out of the total investment amount, so the total investment amount will always have to be greater than the cash amount.