I had the same problem, and for some strange reason, when I ran the report in SQL, it came fine, the problem was when I downloaded the report in .txt | delimited version, and what I did to solve was:

1. create a new report in SSRS, not using table wizard, but Matrix Wizard, and in my case, I was having 1s at the end of the header titles, and after this, the errors went away. I hope this might help.