In GIFTS Online, you are able to specify fields and codes that are required for different record types. If a code is required on the request record, then affiliated reviews will not be able to be saved until that field has been filled out.
To resolve this, you can either fill out the code/field on the request side, or you can stop requiring that field/code.
To make a field not required, you will need to use the Blueprint module, open the appropriate form, and then select the field and mark it as optional on the right hand side.
To make a code not required, go to Admin > Classifications and then select the code. In the upper-right uncheck the 'required" box.