Same problem with v10 and v11.

Solved for v11 with this patch https://github.com/odoo/odoo/commit/77ca51f0892ec62d357e099d5c2a91e580e35383

By now, for v10 I have backported manually. I hope Odoo includes patch in base odoo v10 as soon as possible.

Edited: in my case, server and client are windows 7 laptop.

With ubuntu servers, we have not this problem.

Hello again,

I tried all options but still same result. It seems that lessc is installed incorrectly, I reinstalled everything

from the beginning, but get the same error :(( please help

Use pdadmin：
select * from ir_attachment where mimetype ='text/plain' and datas_fname like '%.js';

Change the value of the mimetype field: text/plain to text/javascript

Clear the browser cache

-----------------

Each time you modify the file, restart the odoo service that you can use

UPDATE ir_attachment SET mimetype = 'text/javascript' WHERE mimetype ='text/plain' and datas_fname like '%.js';

You could:

- Check Odoo logs for any error

- Activate developer mode(will give you better details on the js errors) by setting debug on the url, this chrome extension could help: https://chrome.google.com/webstore/detail/odoo-debug/hmdmhilocobgohohpdpolmibjklfgkbi

- Try with another browser or in an incognito window

- Check if you have nodejs modules installed, this could help you: https://www.odoo.com/es_ES/forum/ayuda-1/question/what-does-this-error-mean-on-odoo-could-not-execute-command-lessc-60439#answer-91689