Uploading from S7-314

I agree with the last few posts, interesting though, I don't expect you to try it but let's look at this in a number of ways.
According to your previous posts this is an existing system but there is a problem that it is not working, assume PLC is in run mode with no errors then it is probably just some sensor or input or wiring that is not in place so it will not start or it stops at a particular point. in this case, if you can monitor using TIA that seems to produce valid code then thats all you need it for.
option 2, Do as Jesper posted remove the red lines, & BLD instructions recompile & see if it matches the PLC (may come up with warnings regarding timestamps but providing there are no differences in actual code you could keep it as a backup, do suggest you do keep the original upload in Classic & the TIA version as it seems the classic accepts the hardware config but not the translated code. So it could be possible if things go wrong you will only have to download the PLC code not the hardware (if TIA allows it).
Option 3, in Classic do the mods, download the code if it seems to work without problems then take another snapshot in Classic.
I do suggest you find the fault first I doubt it is program unless for some reason it is corrupted but not detecting the code error, this I would think is highly unlikely, what with checksums & illegal code detected in the PLC it would surely shut down.
In saying that, I have had a PLC that the code had changed, no possibility of anyone but me going on-line, the code had changed if I remember correctly 3 contacts had changed, can only assume the checksum was the same for the two different versions, almost certain it was corruption that although seems impossible made it valid code. & no, only I had the code, it was password protected (only I knew it as I had changed it a couple of months previously), no lan connection & laptop was always with me as I used to keep it even on holiday to remote in to our Scada systems.

You can do the consistency check. But be aware that this is akin to recompile the program. All timestamps will be renewed. After that you can only go online after download of all blocks which will also set all actual values to the initial values.

I would be cautious about doing that. There may very well be some program issues, but since this is an existing machine which was functioning OK (I guess) the errors cannot have hindered the normal function of the program.

I agree wit Jesper, as he posted it is probably something to do with some change in the past regarding FBD/LAD/STL, I'm pretty sure that removing those errors will still make the logic work as expected, but it is a brave man who changes something when you do not have valid original code.
Jesper has far more exposure to S7 than me in the last 10 years, I was very fluent in S5 but old age & lack of recent programming in S7 I would take Jesper's knowledge as he certainly has more experience than me.

If you need to go online with FC31 to troubleshoot, then I think you can use the 'accessible nodes' to find the PLCs and the blocks, and then rightclick on FC31 and select 'open object'. I think this loads the block into the editor and enters online view mode without trying to convert anything.

'Think' because it is difficult to replicate since you cannot on purpose create blocks with the errors shown.

Thanks again fellas. The reason I've been quiet most of the day is that I made a breakthrough earlier. I found that the normally closed Cycle Stop pushbutton wasn't connected to the PLC. The input was wired to terminals after the pushbutton as if something external used to be in series with it. I jumpered the terminals and things started moving. A classic case of over-thinking it. You were right, Parky but I've been at this long enough to know that it's usually a faulty sensor or actuator. I was so fixated on getting the PLC monitoring working that I missed something fairly obvious.

I'm now facing what appears to be a bad hydraulic proportional valve but I'm not too worried about that as we have plenty of expertise in that area. It looks like there are still a few things not working on the machine (it's a length-measuring tube cut-off saw, by the way) so it may be that wanting to troubleshoot online moves back to the top of my agenda but, for now, my need has receded. To be honest, I'm not sure how helpful an undocumented STL program for an unknown machine will be for fault-finding. That code looks pretty inpenetrable to a Siemens and STL novice.

Yes common problem on used machinery, remote buttons (probably in a small panel that was either on the other side of the machine or somewhere slightly remote to save the operator having to walk round the machine. seen it many times, went to a hydraulic press that had been purchased at an auction, the company who had bought it also purchased a couple of others, the others were ones the company I worked for had done the controls so our label was on the panels, the one they had a problem with was of German manufacture, but I was called in to look at it, the PLC although powered up it was in STOP mode, no power to outputs etc. turned out to be a missing e-stop on the other side of the press, they struggled to understand why the PLC was in stop, the PLC has an input that controlled the run (common on Omron at the time), this was wired into the e-stop circuit, a quick link proved that, fitted a new e-stop, traced the wires for it & hey presto.
If you have the drawings I suggest spending a few hours creating comments on your upload, that way at least you will have some idea of what area of code does what, people here will help if they can if you get stuck.