I can't tell you much, except that "Error NSURLErrorDomain - 999" can be caused by a page reload request, before the previous load had completed. You can sometimes manually create the error by clicking quickly on two links, creating a reload event.
It may be a problem in gmail's code.
> --
> You received this message because you are subscribed to the Google Groups "Gmail-Users" group.
> To post to this group, send email to gmail...@googlegroups.com.
> To unsubscribe from this group, send email to gmail-users...@googlegroups.com.
> For more options, visit this group at http://groups.google.com/group/gmail-users?hl=en.
>