I had the same problems with the Excel Services and found a solution for the office webapps for word and powerpoint also.
Follow the procedure below.
The problem was traced to SharePoint’s built-in URL redirection for various files types. Behind the scenes, SharePoint is attempting to redirect the Excel/Word/Powerpoint file to a common viewer component. We just needed to turn this redirection off.
Edit these 2 files serverfilespowerpoint.xml and serverfilesword.xml and serverfilesExcelServer.xml at the following location: Program Files/Common Files/Microsoft Shared/Web Server Extensions/14/TEMPLATE/XML
Comment out any lines with the file extension of "docx or doc" and "pptx or ppt" and "xlsx or xls "
For Example:
The file "serverfilesExcelServer.xml" should look like this
<?xml version="1.0" encoding="utf-8" ?>
<!– Copyright (c) Microsoft Corporation. All rights reserved. –>
<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>
The file "serverfilesword.xml" should look like this
<?xml version="1.0" encoding="utf-8" ?>
<!-- Copyright (c) Microsoft Corporation. All rights reserved. -->
<ServerFiles>
***<!--<Mapping FileExtension="doc" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" />-->***
<Mapping FileExtension="dot" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" />
***<!--<Mapping FileExtension="docx" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate= "/_layouts/CreateNewDocument.aspx?id=|0" />-->***
<Mapping FileExtension="docm" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate= "/_layouts/CreateNewDocument.aspx?id=|0" />
<Mapping FileExtension="dotx" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate= "/_layouts/CreateNewDocument.aspx?id=|0" />
<Mapping FileExtension="dotm" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" />
<Mapping FileExtension="odt" RedirectUrlTemplate= "/_layouts/WordViewer.aspx?id=|0" NoGetRedirect="TRUE" CreateRedirectUrlTemplate= "/_layouts/CreateNewDocument.aspx?id=|0" />
</ServerFiles>
The same way for the "serverfilespowerpoint.xml" file edit the 2 lines in this file
--> -->
and save both the files.
Perform an IISReset and you will now be able to read and edit the files without any problems.
This will definitely work for you. Cheers and Njoy