In version 5.10.0.5, we accidentally introduced a bug when mapping an 'Amount' field for gifts. The error message presents itself when the gift value in the data source is blank. In this scenario, what should happen is Importacular either ignores the gift from being imported or adds the gift with a $0/£0 value (if that field setting is applied). Instead, the error message 'The reported error was: Index and length must refer to a location within the string. Parameter name: length" is presented in the Control Report.
We have applied a fix which will be available from 5.11, but in the meantime, there is a workaround to ensure that imports can continue.
Go into the field setting for each of your mapped Amounts (often Gift and Receipts Amounts) and apply a data transformation. The purpose of the data transformation is to convert a blank value either into a 0 (zero) or a currency symbol appropriate to your database (so £, $, etc.). The system will then see that there is a value that needs to be ignore/applied.
If you want to import gifts with a zero value, you should use the data transformation that changes a blank value into a currency symbol.
