[Ethereum] Error: new BigNumber() not a base 16 number: when trying to retrieve a string from a mapping

I've created a fairly simple smart contract that has been deployed to the rinkeby testnet. You can see the code below:

pragma solidity ^0.4.18;

contract KVStore {

 mapping(address => mapping(string => string)) store;
 uint MAX_STR_LENGTH = 1000;

 function get(address _acct, string _key) public view returns(string) {
    return store[_acct][_key];
 }
 function set(string _key, string _value) public {
   if (bytes(_value).length <= MAX_STR_LENGTH) {
     store[msg.sender][_key] = _value;
   }
 }

}

I'm using geth to call the set function and then the get function. However, when I call kvstore.get(address, key) I get the following error:

Error: new BigNumber() not a base 16 number: 

I'm not sure whats going on or how to fix. The set function works fine and writes to the rinkeby chain.

I first run this:

geth --verbosity 0 console --rinkeby

Then

var kvstoreContract = web3.eth.contract([{"constant":false,"inputs":[{"name":"_key","type":"string"},{"name":"_value","type":"string"}],"name":"set","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_acct","type":"address"},{"name":"_key","type":"string"}],"name":"get","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"}]).at("0xf8daca377691c8f52b07ef77dfc0e7ca287622c5");

Then

kvstoreContract.set("fly","star",{from:eth.accounts[1]});

Which works fine and sends a transaction to the contract address.

When I try to do

kvstoreContract.get(eth.accounts[1],"fly");

I get the bigNumber error. Any idea why? I'd really appreciate the help.