Spice requires that every node in a circuit have a DC path to ground (ie node "0"). Be careful when, for example, connecting two capacitors at a node. Such a node between caps would have no DC path to ground and would cause Spice to reject the input file. To fix this connect a huge (ie 1 G-ohm or so resistor from the node in question to ground. This will hardly change the circuit but will provide that vital DC path to ground.