Excel Spreadsheet opening in browser – “unable to process your request. Wait a few minutes and try performing this operation again”

If you ever have this issue or a similar one with Word.

Try checking this folder in the 14-hive:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\XML

There are a couple of files to consider.

• serverfiles.xml
• serverfilesExcelServer.xml
• serverfilesPerformancePoint.xml
• serverfilesvisioserver.xml

For my issue. I had one server acting out (not behaving the same way as the other two. Somebody manually changed the content of the file ‘serverfilesExcelServer.xml’ and commented out the first Mapping element

 <ServerFiles>

     <!-- <Mapping FileExtension="xlsx" RedirectUrlTemplate="/_layouts/xlviewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate="/_layouts/xlviewer.aspx?new=1"/> -->

    <Mapping FileExtension="xlsb" RedirectUrlTemplate="/_layouts/xlviewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate="/_layouts/xlviewer.aspx?new=1"/>

    <Mapping FileExtension="xlsm" RedirectUrlTemplate="/_layouts/xlviewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate="/_layouts/xlviewer.aspx?new=1"/>

</ServerFiles>

After I changed the first mapping for xlsx the three servers had the same behavior. This was a head-scratcher especially if some people go around not caring about supported changes and just make manual changes to 14-hive files. Shame on you, if you do!