We can try to replicate this issue. If you send the files to email@example.com, then we can try your files on our end and verify the error.
Datawatch Global Support
In Monarch, you can call your summary a name like "Betty's Music Store", and when you export this to Excel then Monarch does a really good job of turning this into something that Excel allows as a worksheet name like "Betty_s_Music_Store". When you export summaries, you can tell Monarch to make a new file for each key value, or for each filter, so Monarch has to work pretty hard to turn the names you chose for these, or which appear in your data, into valid worksheet table names, or valid Windows file names.
You might find that the error is caused by illegal characters that Windows can't cope with in file names - which include "\", "#", and "$". As well as these characters being problematic anywhere they appear, watch out for filenames with leading or trailing spaces, or files called "." or "..". Basically, if you can manually browse to the folder and create a new file and rename that file as "something.xlsx" or "whatever.txt", then Monarch won't have any problem doing the same.
In Options, where you find the standard export path, it might be worth trying to copy that path and test that you can open it in Windows Explorer. Perhaps the drive letter or the server name of the share might have changed.
Well, I'm having problems again. I'm having a number of exports that run and run for a very long time and never complete. Even though it doesn't complete, it does create an Excel file with 0 bytes when I cancel the export. When I try running it again, that's when I get the error message about the path not being of a legal form. It would appear that the overwrite file when output files exist option is not working properly. I just recently upgraded to Version 18.104.22.16819 32-bit version, and the problem persists even in it.
It seems that my exports are not completing when I have the 'Embed the page Setup header in the worksheet title' option checked. I normally have this and the 'Include Formulas to facilitate editing in Excel' option checked. I've had numerous exports fail when I have both checked, but then it will successfully export it when I uncheck the 'Embed the page Setup header in the worksheet title' option and change the name of the export file (although the export still takes longer than I would expect even for a summary that doesn't really have that many rows and which I had just generated and have displayed). This is something I never had a problem with in Monarch Professional 10.5, but I'm having all kinds of problems with exports in this newest version of Datawatch Modeler. I really need to have this header information appear in my exported spreadsheet, because this is how I document what input file, summary, filter, etc. that I've used for creating the exported spreadsheet. I don't want to have to go back and input this information into the spreadsheet manually after I've exported it.
Although Datawatch Modeler is now handling some huge input files that Monarch 10.5 choked on, in general I've found it to be very frustrating. It seems extremely slow and unstable, and the GUI is a mess and extremely unintuitive. There was absolutely nothing wrong with the old interface. Instead of making my life easier, it's taking me much longer to do things in Modeler than it did in Monarch. And yes, I actually worked through the entire Learning Guide to help with the learning curve due to the major changes to the interface. I actually discovered several things in this Learning Guide that just flat out don't work as advertised in this guide. I've been using Monarch 10.5 for over 5 years, and have become very proficient with it; so the problems I'm having now are very frustrating.
The error message, as you have probably already discovered from the internet, has been baffling people for a few years and seems to have been quite common when xlsx files are in use - as you probably need them to be to do what you want to do.
I recall seeing this a while back when testing a few things for someone else (not this particular problem) but I can't recall whether we found a way around it and if so what it was. I will see if I have any notes - it was not the primary objective at the time.
Are you putting out xlsx or xlsm files? Do you have Excel installed? If so which version/release?
I do recall that attempting to Overwrite seemed to be a connection to the problem. As I recall I simply skipped the overwrite part to carry on with my investigation.