Silly me, tried to use a method that was newer than 10.6…

Author: dmoagx

Source/SPTableRelations.m

@@ -53,6 +53,7 @@ @interface SPTableRelations ()
 
 - (void)_refreshRelationDataForcingCacheRefresh:(BOOL)clearAllCaches;
 - (void)_updateAvailableTableColumns;
+- (void)addAlertDidEnd:(NSAlert *)alert returnCode:(NSInteger)returnCode contextInfo:(void *)contextInfo;
 
 @end
 
@@ -215,15 +216,18 @@ - (IBAction)confirmAddRelation:(id)sender
 			}
 		}
 
-		[[alert onMainThread] beginSheetModalForWindow:[tableDocumentInstance parentWindow] completionHandler:^(NSModalResponse returnCode) {
-			[self performSelector:@selector(openRelationSheet:) withObject:self afterDelay:0.0];
-		}];
+		[[alert onMainThread] beginSheetModalForWindow:[tableDocumentInstance parentWindow] modalDelegate:self didEndSelector:@selector(addAlertDidEnd:returnCode:contextInfo:) contextInfo:NULL];
 	}
 	else {
 		[self _refreshRelationDataForcingCacheRefresh:YES];
 	}
 }
 
+- (void)addAlertDidEnd:(NSAlert *)alert returnCode:(NSInteger)returnCode contextInfo:(void *)contextInfo
+{
+	[self performSelector:@selector(openRelationSheet:) withObject:self afterDelay:0.0];
+}
+
 /**
  * Updates the available columns when the user selects a table.
  */