vSphere machine wont start: Insufficient disk space on datastore

Take a look at all of the datastores visible to the host (in vSphere, select the host > Configuration tab > Storage). Are any of the datastores full or very close to it? The swap file may be located on a full datastore even if the VM is on another datastore and if the host cannot create the swap file, the VM will not boot.

EDIT: Right-click the VM and go to Edit Settings > Options tab > Swapfile location. Select one of the other options ("Always store with the virtual machine" is recommended and will probably work for you since that datastore has a lot of free space). As far as cleaning up that datastore, you can right-click it and Browse and poke around to see what kind of files are taking up the space. It may be likely that your host is configured to use a different datastore for all VMs by default and it is just taken up by swap files at this point.

To change the default swapfile location for the host select the host, click the Configuration tab and Virtual Machine Swapfile Location.

How big is the virtual disk and what is the block size of the datastore? The size of the virtual disk may exceed the allowable size as predicated by the datastore block size.

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003565

Are there any files of the VM stored on other data stores? How full are they? Log into the host and check to see how full the other partitions of the hard drive are.