Dear all
this is a note for all of you experiencing extreme frustrations with installing the Subsites module. I have now spent 2.5 mostly fruitless days on this, before discovering the following remedies are necessary. There have been some seemingly helpful suggestions on this forum dating back 2 years or so, but in the end those remedies did not work for me. Here is a summary of what I have found to work for the localhost

1. the genericdataadmin module may or may not be needed?
2. don't use the Subsites module download marked as latest release Date: 2009-10-01
3. instead - notwithstanding the general notes that it is a preview, may contain bugs, etc. - use the latest Master Build. The version I ended up downloading is dated 2012-03-31
4. extract the Subsites to your root folder. Make sure that the Subsites module does get extracted to a subfolder here! Mine didn't despite following the same extraction method I always use, so I had to quickly locate the folders and files and move them to a new folder called subsites, hoping in the meantime that no other file had been overwritten.
5. go to \sapphire\forms\ folder and find the CheckboxSetField.php file. You will need to then locate the following text at around line 114

if ($source == null) {
$source = array();
$options = "<li>No options available</li>";

and delete the extra = which will otherwise throw an error when you follow the installation instructions at https://github.com/silverstripe/silverstripe-subsites

I have messed around with trying to get this module to install properly for so long, I am no longer sure if any other changes that I made earlier are necessary :((

Good luck!

Found one more problem after successfully getting the module installed on the localhost. I made some mistakes in creating subsites but couldn't search for/delete them.
please see the following post on the problem that is reported. This has worked for me. http://www.silverstripe.org/customising-the-cms/show/16060#post308730

my first post dealt only with getting the Subsites module installed on the localhost.

trying to get it to work on my live server has been another kettle of fish. Namely that I can run dev/build and create the necessary tables, etc. but then am totally unable to access the CMS for my site, even though I am already logged in. I have also cleared the cache, but it doesn't result in anything.

Instead I just keep getting a 500 error that suggests me to reload the page later, or that there is something wrong with the configuration of my website. If I uninstall the Subsites module, dev/build, flush the cache then everything works again.

Ok - here is what I think the problem is. Because I also think that this is related to the fact that I am using a free hosting service, and probably have some limits on PHP memory, I don't think that there is much I can do about it.

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 7680 bytes) in /home/vol3/p4o.net/p4one_10519485/htdocs/sapphire/forms/CheckboxField.php on line 71

Similar fatal error are occurring when I am trying to do other things like add additional PHP templates.

By the way I was able to discover this problem by adding the following line of text

php_value display_errors on

to the htaccess file in the htdocs folder