The search for is a testament to the software's longevity. Despite being nearly a decade old, this version remains the gold standard for developers shackled to legacy JDK 7 environments or proprietary JasperReports Server 5.x installations.
You are using a datasource or feature not present in your server's version. Fix: Go to Tools > Options > General and verify the JasperReports Library version is set to 5.6.0 (not 5.5 or 6.0).
Would you like help finding instead, or do you specifically need the old 5.6.0 installer for a legacy system?