Hi,

I put a calendar block only on the default dashboard or on the home page for all site.
I limit the view block permission for only one system role, auther than "Authentticated user". For example, only "manager" can see the block.

When one page with de block is dipalyed and if the user has not the role with the permission to view the calendar block (not "manager" in my above example), the folowing error occurs :

  Invalid parameter value detected
File: /lib/externallib.php
Line: 332
Stack trace:
Missing required key in single structure: year
Error code: invalidparameter

• line 332 of /lib/externallib.php: invalid_parameter_exception thrown
• line 223 of /lib/externallib.php: call to external_api::validate_parameters()
• line 79 of /lib/ajax/service.php: call to external_api::call_external_function()
   
  I had see the bug for the first time on Moodle 3.8+(Build: 20191205) and I do a test on the lasted 3.8.1+(Build: 20200228) with the same issue.
  It's a similar issue than [MDL-67140|http://example.com,] normaly resolved.
   
  The steps to reproduce the issue are :

1) On the home page, put a calendar block (for all pages in my use case).
2) Limit the block view permission for only one system role, but not "Authentticated user" ("manager" , for example).
3) Connect you whith an user who does not have the role with the permission (not "manager" in my above example).
4) Go to a page where the calendar block is potentialy dispalyed.

Best regards,
Jacques