jar resource may be required in both archetectures

By specifying 'arch' attribute in resources element of jnlp file, you can enforce relaunching into the preferred architecture on 64 bit Windows platforms, when both 64 and 32 bit JREs are installed.

However, if you only (for example) have resources specified for 64 bit arch, and you begin Web Start with 32 bit JRE, then you will get a launch error (No Application Resources) in the 32-bit Java Web Start before the relaunch.