I'm not 100% sure from the description, but I think I'm having a problem similar to this user.
I have a Master-Detail report. Essentially the master's dataset pulls a list of people and passes those individual's identifiers to a series of subreports. When I ran this report on April 2nd, it worked fine with no error messages. When I went to run it today (with 188.8.131.524), I received error messages in place of most of the subreports. The errors indicate that a key field in the subreport's dataset (one that is not included in main report) is not recognized. The subreports, when run as standalone reports, work fine. As this other user suggested, it almost seems like the subreports are ignoring their own dataconnections.
I managed to roll my Standalone Designer back to 184.108.40.206, and now the report runs correctly again.
If I have some time tomorrow I will try to compile the reports and samples of the output to further illustrate the problem. Until then, I hope this can serve as a note that there seems to be a problem with the latest release.