Error when deploy Java Proxy Server EAR to PI

We are trying to deploy our Java Proxy Server EAR to PI using Visual Administrator. However, it gives the following error:

Deploy of the ear has errors :

java.rmi.RemoteException: Cannot deploy application sap.com/TestBatch

Reason: Errors while compiling:

.... .java:91 illegal escape character

if (method.equals("U0024descriptor")) { ....

We have tried to deploy the same EAR to another PI system and it works fine. As a result, we think we might have missed something when installing or configuring this PI but don't have a clue where to start. We have also tried deploying using SDM but also didn't succeed.