Hi
I had the same problem after installing SAP Explorer 4.2 in SAP BO 4.2 SP2, perform the following steps that solved the problem:
1. Stop the tomcat server
2. Stop the SIA agent
3. Delete the contents of folders: work, temp and log located in the directory: C: \ Program Files (x86) \ SAP BusinessObjects \ tomcat
When you delete the content in the 'work' folder will be recompiled all applications.
4. Start the SIA agent
5. Start the tomcat server
I hope will be useful.