save to web (legacy)

For a path error, check every options panel in Save for Web that involves a folder path or filename, and make sure it’s still valid. One way the error can happen is that if settings were carried forward across computers over the years, and you haven’t used Save for Web in a while, it might still be storing a folder path that worked fine on an old computer but doesn’t exist on the current computer. 

The two images I posted below are examples of where a filename or path can be specified in Save for Web (Legacy) for slices. For example, in the second image, if the Background Image folder path is invalid that might cause a path error. Or maybe an invalid character in a filename might cause it too. If you still get the error keep looking for more places in Save for Web where a path or filename can be entered because there might be more than the ones I found below. 

Legacy Save for Web is based on a zombie technology called Image Ready which hasn't existed in more than 20 years. Back in the early days of the internet, Image Slices were a hack necessitated by dial-ups and painfully slow-loading web images. We haven't had any need for that since broadband/DSL was introduced.

Instagram:

• Instagram posts can be square, landscape, or vertical. All images will be cropped to a square in the feed.
• The ideal size for square posts is 1080px by 1080px at a 1:1 aspect ratio.
• For landscape posts, use an image that is 1080px by 566px, with an aspect ratio of 1.91:1.
• Vertical images should be sized at 1080px by 1350px with a 4:5 aspect ratio.

In Photoshop, use File => Export => Export As to save optimized images for the web.

Double check that the save location is valid and or try a shorter location (path).

I have a couple of Instagram carousel scripts which might help:

https://community.adobe.com/t5/photoshop-ecosystem-discussions/exporting-carousels-ruined/td-p/15073529#M846879

https://community.adobe.com/t5/photoshop-ecosystem-discussions/exporting-carousels-ruined/td-p/15073529#M846880