Unfortunately if you are experiencing Snow Leopard could not validate source error then you need to take proper course of action else the situation would gone much more cumbersome. This would result to serious inaccessibility to their files and folders. In most cases, this error appear due to damaged ISO or ISO is being running wrong file system. This error actually represents that Mac is incapable to validate in writing at storage media. For resolving the issue one can try creating new ISO after deleting the older one. Many time ISO becomes corrupted because of disk issues which can be sorted out through repairing disk by disk utility. This way you may resolve snow leopard could not validate source. Whenever there is data loss happen then you should go with data recovery for which you can use latest backups of drive if available. Otherwise consider Mac Data Recovery Software for regaining corrupted, formatted or damaged data comfortably. It is fully equipped with highly sophisticated or robust scan algorithm which can resolve adverse situation arises in Mac. Moreover the tool supports all the Mac OS X edition. So you can fix snow leopard could not validate source issue by this manner.