Understood, here it goes:
A few hours ago we received important information from SolusVM support regarding problem mentioned in the topic. This information should be helpful for some of you. This is a solution for the problem with server rebuild returning 'Invalid Template' error.
"Here is the patch you need to run on the master node in SSH:
wget http://files.soluslabs.com/solusvm/fixes/api_vserver_rebuild.txt -O /usr/local/solusvm/includes/api/api_vserver_rebuild.php
This will allow you to rebuild KVM virtual servers via the API. Example output if using the json return values would be:
{"status":"success","statusmsg":"Virtual server is being rebuilt","rootpassword":"6axLkKpi","information":"Blah\nBlah\nBlah"}"
According to the answer received from SolusVM support, this solution works only on SolusVM beta and it will be included in the stable version.