I’ve been looking for the solution to this problem on and off for months, and finally stumbled upon the answer.

The scenario was this:

I placed an SSRS report into a PPS dashboard. The SSRS report has nothing but a gauge, and a table with some related data. For some reason the gauge image only shows up when I have the “show toolbar” option checked, otherwise the gauge shows up as a broken image or red x. In either case, the data for the table always shows up. If I navigate to the report server directly and view the report I have no problems, it only seems to happen from within PPS (both in designer and once deployed).

Apparently when Reporting services is configured to authenticate via “Trusted Account” mode, you need to specify the URL of the Report Server proxy rather than just the URL to the Report Server.

So for example, when configuring the “Report Server URL” in your Performance Point SSRS report you would typically enter it as

http://server/reportserver

however if you’re experiencing the problem described above, try referencing it including _vti_bin in the URL like so

http://server/_vti_bin/reportserver

That seemed to do the trick for me. Hope this saves someone some frustration.