diff --git a/api-openbis-python3-pybis/src/python/pybis/dataset.py b/api-openbis-python3-pybis/src/python/pybis/dataset.py
index cbc21fe60a2edab578fb3dfc7a0d7d95f7c5d085..8222f8de6e855d1bac388367193a1add526664e2 100644
--- a/api-openbis-python3-pybis/src/python/pybis/dataset.py
+++ b/api-openbis-python3-pybis/src/python/pybis/dataset.py
@@ -950,11 +950,11 @@ class DataSet(
 
     def _upload_v3(self, data_stores):
         upload_id = str(uuid.uuid4())
-
+        datastore_url = data_stores["downloadUrl"][0]
         # for uploading phyiscal data, we first upload it to the session workspace
         self.upload_files_v3(
             upload_id=upload_id,
-            datastore_url=data_stores["downloadUrl"][0],
+            datastore_url=datastore_url,
             files=self.files,
             folder="",
             wait_until_finished=True,
@@ -986,6 +986,7 @@ class DataSet(
                 "@id": "4",
                 "permId": self.sample.permId
             }
+        # TODO: check if this part is needed
         parent_ids = self.parents
         if parent_ids is None:
             parent_ids = []
@@ -1003,7 +1004,8 @@ class DataSet(
             "params": [self.openbis.token, param]
         }
 
-        resp = self.openbis._post_request(self.openbis.dss_v3, request)
+        resp = self.openbis._post_request_full_url(urljoin(datastore_url, self.openbis.dss_v3),
+                                                   request)
         if "permId" in resp:
             permId = resp["permId"]
             if permId is None or permId == "":
@@ -1200,6 +1202,7 @@ class DataSetUploadQueue:
     """Structure for uploading files to OpenBIS in separate threads.
     It works as a queue where each item is a single file upload. It allows to upload files using v1
     and v3 api. V3 api uses multipart schema for file upload, whereas V1 api makes sue of the body"""
+
     def __init__(self, workers=20, multipart=False):
         # maximum files to be uploaded at once
         self.upload_queue = Queue()
@@ -1313,6 +1316,7 @@ class ZipBuffer(object):
 
 class DataSetDownloadQueue:
     """Special queue structure for multithreaded downloading files using V1 API."""
+
     def __init__(self, workers=20, collect_files_with_wrong_length=False):
         self.collect_files_with_wrong_length = collect_files_with_wrong_length
         # maximum files to be downloaded at once
diff --git a/ui-admin/src/core-plugins/admin/1/as/services/xls-import/xls-import.py b/ui-admin/src/core-plugins/admin/1/as/services/xls-import/xls-import.py
index f4701403e38d03065b3097e9cf15199dcc1e6411..753da629c6a1ce3d97175bf08486fba941e46b29 100644
--- a/ui-admin/src/core-plugins/admin/1/as/services/xls-import/xls-import.py
+++ b/ui-admin/src/core-plugins/admin/1/as/services/xls-import/xls-import.py
@@ -62,7 +62,7 @@ def process(context, parameters):
                     tempPath = singleFile.getAbsolutePath()
             byteArrays = MasterDataRegistrationHelper.getByteArrays(Path.of(tempPath), ".xls")
             if len(byteArrays) == 0:
-                raise UserFailureException('No .xls or .xlsx fields found. These should be on the root folder of the zip file.')
+                raise UserFailureException('No .xls or .xlsx files found on the root folder of the zip file. This error could be caused by the way the zip file was generated.')
             parameters.put('xls', byteArrays)
             allScripts = MasterDataRegistrationHelper.getAllScripts(Path.of(tempPath))
             parameters.put('scripts', allScripts)