Hi HireSpace,
a) The negative impact depends on:
- Is there traffic landing on this page from any outside channel (organic, referral, paid marketing)
If so, then yes it is probably hurting your site. If a visitor sees a 403 page a common response is to go directly back to the referring page, i.e. they leave your site.
- Did the 403'd page have external links pointing to the page?
If yes, then a 403 error would cause the link authority to drop, since you do not redirect that page to another page on your site.
- As far as SEO is concerned, no this isn't negatively impacting your site.
When Google sees a 403 error they pretty much handle it like any other 400 error. They wont penalize you, however, having a lot of 400 errors could be an indication of poor usability and we know how Google loves to introduce new ranking factors for the SERPs.
b) Can I fix it?
Yes, I suggest, for any page removed from your site, that you 301 the page to its closest related page. This tells G that the page is permanently moved to a new page, pass any authority to that page, and anyone landing on the old page is automatically redirected to the new page. You'll see the 403 errors decrease as G crawls your site and recognizes the 301 redirect.