The optional field can be defined as different types of data. If you have added the field to a column editor, you have to be really careful to select the matching field type. Before you reinstall, I have another suggestion.

Edit the QIWIN.INI file using a text editor and remove your modifications to grids. For example, you may have a section for, [grdInvoiceList]. Remove the entire section. Now try editing your batch again.