1. Open up the Project record and select the 'Account Restrictions' tab
2. Verify whether this account is allowed to use the project
3. If the account is not allowed to use the project, add the account to the list of selected accounts OR if the account is already within the list of selected accounts, change the setting from 'Allow use of selected accounts' to 'Allow use of all account's, save the project record, and then change the setting back from 'Allow use of all accounts' to 'Allow use of selected accounts' and validate the import again.