This is NOT {site_dir}/templates but {deploy_dir}/templates that you have to use when you deploy a website into a specific directory.

If you have put a value in the "deploy folder" then
Solution 1 (make subdirectory with symbolic links)
- Folder tabs / set action = "special copy"
- Common tabs / template folder = {deploy_dir}/templates

Solution 2 (make subdirectory with a copy)
- Folder tabs / set action = "copy"
- Common tabs / template folder = {deploy_dir}/templates

When the common "deploy folder" is empty, again 2 solution but replace {deploy_dir} by {site_dir}
- Folder tabs / all action = "ignore"
except action for templates = "special copy"
- Common tabs / template folder = {site_dir}/templates



Concerning the PHP Fatal error, can you confirm that you are using the latest JMS 1.3.29.
If this is not the case, see the FAQ for the procedure to get the latest version.
www.jms2win.com/en/faq/faq-joomla-multi-sites#cat-122

I do confirm that I am using the latest JMS 1.3.29.

I changed into {deploy_dir}/templates, but the problem remains unchanged.
The configuration is :
- Main site : /local/Joomla_3.2.1
- Slave site : /local/Joomla_3.2.1/multisites/slave2

Slave template :
1. Common :
- Domain names : http://{site_url}/multisites/{site_id}
- Directories :
--- deployment : {site_dir} which is the same than {multisites}{site_id}
--- template directory : {deploy_dir}/templates

2. Files and directories :
- templates : copy

Thanks a lot for your help .

Based on what I read here, it seems that the definition that you did is
Site ID = slave2
Template = xxxxMultisites

I also see local in the path.
I am wondering if you are working on a "localhost" of if you are working on internet.

Which platform do you use ?
Do you use a linux, or windows or something else ?

When you check the files and folder on the disk, do you have a physical directory for
/local/Joomla_3.2.1/multisites/slave2/templates
or a symbolic link
or a physical directory with inside symbolic links.

The expected result is a physical directory for the "/templates" directory and inside either a copy or symbolic link depending on the JMS action on /templates (copy or special copy).