I've installed the new JCE version on the master site.
Then I applied the patches of multisites.
When I want to install this new JCE version on the slave site, I get the error

The version of the extension is not identical to the one installed by the master site.
(Found version: '157' expected: '1.5.0 Stable')
Installeer Component Fout


Can anyone help me ?

First, which version of JMS are you using.
If the version is prior 1.1.19, there is a fix that could explain that.
In this case, update JMS to get the latest version
See procedure described in the FAQ www.jms2win.com/faq

Otherwise, check in Joomla install the version corresponding to the extension.
JMS has detected a problem of version concerning this extension and it is require to check the reason.
Perhaps you could send me by email the extension that you try to install to allow me review the content of the zip.

Do you have another extension that have a similar name than JCE present in your environement ?