​@DERYNGVE I don’t know exactly why you are getting that error for that particular report, but I think what may be happening is that there is a field that was merged across more columns than are currently in one of your report tables.  If you open the rdl in a text editor, you could search for “spanned>22” to see if you can pinpoint the issue.  

Other than that, it may be helpful to know what the report is.  Did you customize it?  Does it give the same error if you open it while in the new version of the Report Designer but are not connected to an IFS instance?  Did you update your IFS version or just the Report Designer version?