Generic error occurs when replying to a Copy Request if you don't have permissions to send a reply

[alawvt]

Describe the bug
A clear and concise description of what the bug is. Include the version(s) of DSpace where you've seen this problem & what web browser you were using. Link to examples if they are public: DSpace 7.3, Firefox

1. With a personal email, I created an item in DSpace 7 Demo, https://demo7.dspace.org/items/b2fac597-a382-4c0e-82ef-802afca015a0.
2. As dspacedemo+admin@gmail.com, I restricted the bitstream, https://demo7.dspace.org/items/b2fac597-a382-4c0e-82ef-802afca015a0/request-a-copy?bitstream=bfe2b22e-bca7-4a13-851e-f8f6f5091ec4 to Administrators only.
3. I requested the item from a second personal account.
4. I received the request at the first personal email account. I selected "Send copy" and received the error,
   

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Expected behavior
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Related work
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[tdonohue]

I tested this today and "Request a Copy" is working fine for me locally.

However, I have seen this scenario before, and I suspect you are hitting an authorization issue. For instance, I've seen this same behavior when performing these steps:

1. Login as "User1" and submit an Item with a restricted Bitstream
2. Login as "User2" and submit a "request a copy" request to User1 for access to that Bitstream
3. Now, login as a full Admin (User3) and attempt to reply to that request. User3 can access the "Request a Copy" page, but the reply will fail, because only the user who received the request (Submitter by default) can reply to it.

The person who receives the request depends on your "strategy" configured for Request a Copy. By default, only the original submitter can reply. But, it's possible to specify a different responder if you change the request configuration to use "helpdesk email" or Collection Administrators or Item metadata. See https://wiki.lyrasis.org/display/DSDOC7x/Request+a+Copy#RequestaCopy-SelectingRequestaCopystrategy

All that said, I think the bug here is that the error message returned is not informative. Additionally, the permissions of the user accessing the request a copy page should be checked earlier & you should be blocked from accessing the page if you are not allowed to respond. I'll update this ticket's title to clarify the bug.

[tdonohue]

This appears to be fixed in 7.6 by #2199