diff --git a/API/Routes/Case/CaseRoute.py b/API/Routes/Case/CaseRoute.py
index d95482f41..5750fb276 100644
--- a/API/Routes/Case/CaseRoute.py
+++ b/API/Routes/Case/CaseRoute.py
@@ -433,6 +433,8 @@ def prepareCSV():
 def downloadCSV():
     try:
         casename = session.get('osycase', None)
+        if not casename:
+            return jsonify({'message': 'No active case session.', 'status_code': 'error'}), 400
         dataFile = Path(Config.DATA_STORAGE,casename,'export.csv')
         
         dir = Path(Config.DATA_STORAGE,casename)
diff --git a/API/Routes/DataFile/DataFileRoute.py b/API/Routes/DataFile/DataFileRoute.py
index 2b7e98eff..dceb7636d 100644
--- a/API/Routes/DataFile/DataFileRoute.py
+++ b/API/Routes/DataFile/DataFileRoute.py
@@ -160,17 +160,9 @@ def validateInputs():
 @datafile_api.route("/downloadDataFile", methods=['GET'])
 def downloadDataFile():
     try:
-        #casename = request.json['casename']
-        #casename = 'DEMO CASE'
-        # txtFile = DataFile(casename)
-        # downloadPath = txtFile.downloadDataFile()
-        # response = {
-        #     "message": "You have downloaded data.txt to "+ str(downloadPath) +"!",
-        #     "status_code": "success"
-        # }         
-        # return jsonify(response), 200
-        #path = "/Examples.pdf"
         case = session.get('osycase', None)
+        if not case:
+            return jsonify({'message': 'No active case session.', 'status_code': 'error'}), 400
         caserunname = request.args.get('caserunname')
         dataFile = Path(Config.DATA_STORAGE,case, 'res',caserunname, 'data.txt')
         return send_file(dataFile.resolve(), as_attachment=True, max_age=0)
@@ -182,6 +174,8 @@ def downloadDataFile():
 def downloadFile():
     try:
         case = session.get('osycase', None)
+        if not case:
+            return jsonify({'message': 'No active case session.', 'status_code': 'error'}), 400
         file = request.args.get('file')
         dataFile = Path(Config.DATA_STORAGE,case,'res','csv',file)
         return send_file(dataFile.resolve(), as_attachment=True, max_age=0)
@@ -193,6 +187,8 @@ def downloadFile():
 def downloadCSVFile():
     try:
         case = session.get('osycase', None)
+        if not case:
+            return jsonify({'message': 'No active case session.', 'status_code': 'error'}), 400
         file = request.args.get('file')
         caserunname = request.args.get('caserunname')
         dataFile = Path(Config.DATA_STORAGE,case,'res',caserunname,'csv',file)
@@ -205,6 +201,8 @@ def downloadCSVFile():
 def downloadResultsFile():
     try:
         case = session.get('osycase', None)
+        if not case:
+            return jsonify({'message': 'No active case session.', 'status_code': 'error'}), 400
         caserunname = request.args.get('caserunname')
         dataFile = Path(Config.DATA_STORAGE,case, 'res', caserunname,'results.txt')
         return send_file(dataFile.resolve(), as_attachment=True, max_age=0)
diff --git a/test_issue_356.py b/test_issue_356.py
new file mode 100644
index 000000000..544ff8774
--- /dev/null
+++ b/test_issue_356.py
@@ -0,0 +1,52 @@
+"""
+Test for Issue #356: Download endpoints crash with TypeError when no case session is set.
+Verifies that all 5 download endpoints return 400 JSON instead of crashing with TypeError.
+"""
+import sys
+import os
+
+# Add project root so imports resolve
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'API'))
+
+from API.app import app
+
+
+def run_tests():
+    app.config['TESTING'] = True
+    client = app.test_client()
+
+    endpoints = [
+        ('/downloadDataFile', 'GET', {'caserunname': 'test'}),
+        ('/downloadFile', 'GET', {'file': 'test.csv'}),
+        ('/downloadCSVFile', 'GET', {'file': 'test.csv', 'caserunname': 'test'}),
+        ('/downloadResultsFile', 'GET', {'caserunname': 'test'}),
+        ('/downloadCSV', 'GET', {}),
+    ]
+
+    passed = 0
+    failed = 0
+
+    for path, method, params in endpoints:
+        resp = client.get(path, query_string=params)
+
+        if resp.status_code == 400:
+            data = resp.get_json()
+            if data and data.get('status_code') == 'error':
+                print(f"PASS: {path} -> 400 JSON error")
+                passed += 1
+            else:
+                print(f"FAIL: {path} -> 400 but unexpected body: {data}")
+                failed += 1
+        elif resp.status_code == 500:
+            print(f"FAIL: {path} -> 500 (TypeError not fixed!)")
+            failed += 1
+        else:
+            print(f"FAIL: {path} -> unexpected {resp.status_code}")
+            failed += 1
+
+    print(f"\nResults: {passed} passed, {failed} failed out of {len(endpoints)}")
+    sys.exit(0 if failed == 0 else 1)
+
+
+if __name__ == "__main__":
+    run_tests()