1. There should be an expense incurred on the account you selected on the Source tab for the month you specified
2. Transaction expenses incurred on the Source tab should have the same value specified for the Name, Department, Class or Location when entered.
Note: Please check the expense account you are trying to allocate if there are by the Reports available in Netsuite such as the General Ledger or Income Statement Detail Report for the month/period specified (Reports> Financial).