RN31400

You have given very few details concerning your issue.  "It comes up with an OS error" is like calling an an auto mechanic and telling him simply "my car doesn't run" and expecting him to diagnose your problem over the phone.  In addition, many of us don't use a Mac (myself and StephenB are major posters, and neither of us do), so can't help even if you give details.

You can start with these:  Is the error on the NAS or the Mac?  What is the error?  What NAS user name are you using (admin, or your own account)?  Did this start happening when you updated the OS on the Mac or NAS, and if so, from what to what?

Your non-descriptive subject, which doesn't even mention Time Machine, certainly doesn't cause anyone who might know the answer to look at this post.

Apple apparently makes changes to Time Machine all the time and just expects other companies to keep up with them.  Or maybe they hope other companies won't, forcing you to use their products exclusively.  I've come to that conclusion based on other posts here similar to yours, but much more descriptive.  So, maybe, you'd get a better answer in an Apple forum. 

Start by helping forum users understand the specifics of your issue, and maybe you'll get better responses.  But this is primarily a user-to-user forum, and your attitude of just expecting a solution from a fellow, unpaid user is not going to gain you friends here.  JeraldM does work for Netgear and did start trying to help you, and you didn't indicate you did read the article he pointed you to nor did you post the information he asked for.  I can certainly understand why he would abandon trying to help you when you won't even help yourself.