Index: branches/5.2.x/core/install/upgrades.php
===================================================================
--- branches/5.2.x/core/install/upgrades.php
+++ branches/5.2.x/core/install/upgrades.php
@@ -2058,6 +2058,11 @@
 			$table_name = $this->Application->getUnitOption('email-template', 'TableName');
 			$fields = $this->Conn->Query('DESCRIBE ' . $table_name, 'Field');
 
+			// The "_renameTables" method doesn't rename IDField, so find real one in DESCRIBE result.
+			if ( !isset($fields[$id_field]) ) {
+				$id_field = 'EventId';
+			}
+
 			if ( !isset($fields['l1_Body']) ) {
 				// column dropped - nothing to convert anymore
 				return;