Is this issue only with offline files? We do have limits on path length (1024 bytes) and this should hold for any file path. Windows also have path limit (http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath) of 260 unless some special syntax is used. I see you are using path with prefix ("\\?\UNC\") which allows the client to send long paths (upto 32767 cahracters) and ontap does not support such long paths. I believe this is the same behavior in 7-mode as well. Is this change of behavior from 7-mode?
Re: NetApp C-Mode (8.2) :- Unable to open offline file having file path greater than 1040 chars