Are you using the latest stable version of UBCD? No 4.1
maybe that is the workaround you should be searching for?
Maybe you would like to try downloading the latest stable? Download it, check its MD5/SHA1 checksums, burn it in 4x or 8x, verify it was correctly burned and check if it is working as it should, or if you still have problems.
Have you searched for similar problems so to find a solution? Yes, but I didn't find any.
There were some reports in the past, but I think most of them were resolved before the current stable version. Still, if you find problems with the latest stable, please report back so to find a solution.
Are you using the Syslinux menu or the Grub4Dos menu? Good question, I just burned it and boot from it
The current stable version uses the Syslinux menu as default (the one you see when you "just boot it"), but you can select an alternative menu, the Grub4Dos menu, which in some specific situations could be helpful. It is not "better", just an alternative.
Have you tried different FDUBCD boot options? Don't know what that means
I'll be quoting here an old post from Icecube that was related to some Opcodes messages:
If memdisk floppy emulation doesn't work for you, can you write down the 'invalid opcode' that you get, and try all boot options of the freedos image with memdisk emulation:
0 Boot Clean
1 Boot UMBPCI (silent)
2 Boot UMBPCI (optimal)
3 Boot UMBPCI (semi-defensive)
4 Boot EMM386 (optimal)
5 Boot EMM386 (semi-defensive)
6 Boot no UMB (defensive)
7 Boot no UMB (ultra-defensive)
And report which 'invalid opcodes' you get, and which entries boot.
Then try the same when using grub4dos floppy emulation.
So that the developers of memdisk can fix this issue.
Also try to run in from CD and USB, report the differences.
Those alternatives are presented when you select some DOS-based tool in UBCD that starts with the UBCD DOS boot menu.
But again, this was posted before the current stable version, so please try the latest stable UBCD first, and don't hesitate in reporting here your feedback (whether the problem is solved by using the latest stable UBCD version or not).