I just tried with one of my Blockchain wallets, and it worked fine.
1st troubleshooting idea: are you sure you're putting the lengthy and random identifier on the URL, and not the wallet nickname?
2nd troubleshooting idea: if the password contains spaces or other special characters, they may need to be encoded to conform with the specification for URLs. Some browsers do the conversion automatically, for others you'll need to encode it yourself using a service like http://meyerweb.com/eric/tools/dencoder/