Tell us what you are trying to do?
Install the plugin
Is there any documentation that you are following?
na
Is there a similar example that we can see?
na
What is the link to your site?
as above
When I try to install the Toolkit Access plugin I get a 503 error alll other extensions have installed ok.
From the list of plugins click the register link for any of the existing Toolset plugins, and that will take you to the custom installer page where you can register the site and choose which plugins to install.
If the error is coming from something like a PHP upload size limit then the custom installer won't be affected.