Gantt stop working

Hello there

my Gantt chart stopped working. I am getting the following error:

Traceback (most recent call last):
File “/home/frappe/frappe-bench/apps/frappe/frappe/app.py”, line 62, in application
response = frappe.handler.handle()
File “/home/frappe/frappe-bench/apps/frappe/frappe/handler.py”, line 22, in handle
data = execute_cmd(cmd)
File “/home/frappe/frappe-bench/apps/frappe/frappe/handler.py”, line 53, in execute_cmd
return frappe.call(method, **frappe.form_dict)
File “/home/frappe/frappe-bench/apps/frappe/frappe/init.py”, line 939, in call
return fn(*args, **newargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/client.py”, line 300, in get_js
with open(contentpath, “r”) as srcfile:
IOError: [Errno 2] No such file or directory: u’./assets/frappe/js/lib/frappe-gantt/frappe-gantt.js’

how could I solve this?

I checked all the files are there.

kind regards,
S.