Hi Nutty,
Is the Java set on auto upgrade? If yes, you might have to check if the current update is compatible with BO XI 4.1 SP3.
For example: it might happen that report is working fine with Java 6 Update 8 but starts giving issue with Java 6 Update 20. I am just giving a scenario.
To test it, you can check if issue comes in Rich client and Interactive editing mode in BI Launchpad.
If it works with Rich client and Interactive mode then you can probably try checking which Java version + upgrade is compatible.
Also check if it is coming with multiple users on multiple machines. If yes, just compare their java versions. It could help you in reaching the root cause.
Does the issue comes on BO server? I mean if you remote log onto server and check. If not, you can compare the java version and upgrade among server and client and then check.
Regards,
Yuvraj