If you have a problem with file synchronization not deleting files, it may be because you have a file that is longer than 255 characters. I had this problem, found a .url file more than 255 characters, manually deleted it, and sychronization with delete now worked.
The Windows recycle bin has issues with long file paths sometimes, especially when passed a list of files from multiple locations. It's a longstanding bug in the OS. (As well the more normal case where it may say it can't handle a really long path and will need to delete the file normally, there are also cases where Windows simply skips over the files and does not delete or recycle them at all, and also does not tell you or the application -- i.e. Opus -- that it did so.)
If you're having problems, disabling the recycle bin temporarily should allow the files to be deleted via the Sync panel. (Preferences / File Operations / Deleting Files)
Thanks, Leo. Actually, the file name was around 158 characters with an URL file extension. I was not even able to delete it manually, but I was able to rename it with fewer characters. After I deleted it, Dopus file synchronization worked fine. There is also a program called Long File Names Finder by DCsoft.com which will search for file names for any number of characters you wish. You can also use a program called AccessEnum by SysInternals.com which will show you files that have permissions which cannot be read because of their file name character length.
Were you deleting to the recycle bin, or bypassing it?
The recycle bin has some quirks at times. It's also not just the name length but also the total path length. (Both can cause issues with the recycle bin.)
Deleting without the recycle bin means Opus handles everything itself, and we design Opus to cope with very long file names in all simple operations (copy, move, rename). (With more complex operations, we aim for things to work, but can't always guarantee it since not all OS and library APIs support such things.)
Opus can also search for things by path length. So you should not need any external tools to deal with or find things with very long names, but you may need to bypass the Recycle Bin.