This article will help resolve your issue.
Make sure all PDF files attached in your return (Investment income section) have unique names and none have any special characters e.g #, $, etc. or spaces in the file name.
It sure would be nice if TurboTax would warn you if your filename was not valid. My original attachment was named "1099-B.pdf" and was rejected with this error. I'm hoping the dash "-" character is one of the etc/... special characters that aren't explicitly called out.
It seems there may be a deeper issue. I have deleted the 1099B attachment and refiled with the pdf named "MyName1099B.pdf" and simply "schwab.pdf", both were rejected with this error. I have no way of viewing what the XML file's contents are but am guessing that's where the issue lies?
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I was able to find a workaround to this issue. I was entering my 1099B amounts as a summary of all sales total, if you enter each sale individually you are not required to upload the form. This may be cumbersome if you had a lot of sales but at least it avoids the issue.