I have selected single company only. actually I was getting 'Access error for res.partner' while making invoices in second company. to fix this I have added user group in res.partner in company model, with this I was able to fix access error but by doing this my contacts are visible in both companies. if I remove user group from 'res.partner' model contact won't be shared in both companies and I'll get security access error. I guess this is BUG. I have added screen shots in my post.

I doubt that it's a bug - there were a few issues last year after this was changed in Odoo 13, but it should be OK now.

The error message seems to be telling you that you can't access the contact record for the company. Is the company blank on that contact?

Thanks for sharing this post. I am in a multi-company environment, and run into the same problem (error message) whilst trying to segregate some contacts to its own company.

I have disabled the "res.partner company" option to set the company, then turned the option back on afterward. Would like to ask if this would cause any trouble doing that?

The contact that I set the company field, are actually the company that is in the group. Would anyone know whether this will cause problem with the inter-company transactions?

Hello Chris, is it the same for V15? I have multi-companies and users from one company only can view all contacts. How can I fix this?

hi friends, i found the same problem on odoo ce 13. contacts by default visible to all companies in the same database.