If you get error message “HTTP Status 400 – Invalid Path /Analytical Reporting/WebiView was requested. The request sent by the client was syntactically incorrect.”, it is very likely that you are using IE 9.
IE 9 is not supported yet by BO. It is planned to be supported in BO BI 4.1 and BOE XI 3.1 SP5 that will be released somewhere in Q1 2012.
bukhantsov.org 
I was running into the same error when “they” upgraded my laptop with IE9. I found this workaround, and it is working for me.
http://www.forumtopics.com/busobj/viewtopic.php?t=170250&postdays=0&postorder=asc&start=43
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Yes, that was perfect solution at that time. I used it on several systems and it worked fine. (If it concerns one laptop, an easier workaround is to downgrade IE.)
Currently the most correct solution is to install SP5, it supports IE9; If you also install FP5.3, Java 7 will be supported.
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