Pessoal, muitas pessoas tem problemas para iniciar o FrostWire devido ao Java, muitas vezes o problema surge pela falta do Java Runtime Environment.

Os erros são os seguintes:

#
Starting FrostWire...
#
Java exec found in PATH. Verifying...
#
OOPS, you don't seem to have a valid JRE. FrostWire works best with Sun JRE available at http://www.java.com
#
OOPS, unable to locate java exec in /usr/lib/ hierarchy
#
You need to upgrade to JRE 1.4.x or newer from http://www.java.com
#
ls: /usr/java/j*: No such file or directory
#
OOPS, unable to locate java exec in /usr/java/ hierarchy
#
You need to upgrade to JRE 1.4.x or newer from http://www.java.com
#
ls: /opt/j*: No such file or directory
#
OOPS, unable to locate java exec in /opt/ hierarchy
#
You need to upgrade to JRE 1.4.x or newer from http://www.java.com

ou

Something went wrong with FrostWire.
Maybe you're using the wrong version of Java?
(FrostWire is tested against and works best with with Sun's JRE, Java 1.4+)
The version of Java in your PATH is:
java version "1.6.0"
OpenJDK Runtime Environment (build 1.6.0-b10)
OpenJDK Client VM (build 1.6.0-b10, mixed mode, sharing)

Esses problemas podem ser facilmente resolvidos com o comando:

sudo update-alternatives --config java

Após isso, selecione a opção que inclua "sun" no nome.

Pronto!

Retirado do site: FrostWire - Ubuntu.com