You cant revert back to an older version after an upgrade is made by simply replacing the old files. You need to revert the DB structure too. Because during the upgrade elgg sometime modifies the DB structure, the Data storage structure and modifications in some other plugins etc.. The best solution for you to is move to 1.7.15 and fix the error with site access plugin.
@All : Donot upgrade / install new plugins in your production server with out testing it in a test server/local host.
lol. silly me didn't restore my elgg data folder from backup. Solved the issue.
@Team Webgalli Thank you.
set 'count'=>true for elgg_get_entities_from_relationship() function.
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