Concerning the error reported on admin.multisites.php on line 37 corresponds to a call for Joomla 1.6! and not for Joomla 1.5.14.
It seems that you have a joomla 1.6 version file.
The global joomla version number returned is >= 1.6 or another extension change the JVERSION environment parameter.
So it seems that you have a Joomla 1.5.14 installed and that the version number provided is 1.6 or higher (that is inconsistent).
JMS is able to install files using the Joomla FTP Layer.
So if you have enabled the FTP connection in the global configuration, it will be used by JMS to perform the installation.
See tutorial video 15 that show how to use the FTP Layer.
/tutorial#jms12x-15