When I am using Link to Outlook and I attempt to search for a particular request to attach the email/document to, the field displaying the request in question turns into a red square with a big red X.
The inability of Links to Outlook to view this request almost always lies with something wrong in the request record. Accidental tabbed or manual extras spaces between words of after sentences create whitespace that are hard for the Links add-in to read and will result in the red 'X' that you are experiencing. Remove this extra space and ensure that after every end of sentence punctuation there is no space and save the record.
Restart outlook and attempt the link again; searching for the record this time should result in no red x and should allow you to link this message to the activity in GIFTS successfully.