In some cases when a user with full control clicks the Pending Requests page (/Access%20Requests/pendingreq.aspx) Image 1 below – s/he may receive an error “Sorry, this site hasn't been shared with you” (Image 2).

There are couple of options (see the end for reference) how to resolve this issue – this article walks you through using SharePoint Designer to resolve this issue. I personally find this option easier :-).

Image 1

Image 2

Here are the steps to resolve the issue:

  1. Open the site in SharePoint Designer > All Files > Access Requests List (Image 3)
Image 3

2. Right click the Access Requests > Properties (Image 4)

Image 4

3. Click Permissions for this list (Image 5)

-          - List permissions page opens in the browser

      -        Add the necessary permission - SharePoint group which has full control to this site. 

Image 5

        Have the owner test out now. This should resolve the access denied error. Hope this help!

        Here is another approach to resolve this issue – even though this Microsoft KB talks about SharePoint Online; I was able to resolve on-premise issues following the approach.

       "Access Denied" to Access Requests list or “Request approval failed” when you process a pending request in SharePoint Online