Zitat
Got this from an outside source and thought I would share 
In Windows 7 you have to edit the registry to remove DDE completely. This should work for Vista too. Check the "Ignore other applications that use Dynamic Data Exchange (DDE)" box in Excel -> Excel Options -> Advanced This alone might work for you by itself - didn't for me, I got an error every time I double-clicked on an excel document. BACK UP your registry.
Open regedit, browse to
HKEY_CLASSES_ROOT\Excel.Sheet.8\shell\Open
delete the ddeexec key, (or just rename it if you are worried - i just renamed it and it worked) Then click on the "command" key and replace the /e on the Default and command string in that key with "%1" Quotes around %1 are important. NO QUOTES MEANS NO WORKIE!!!!
HKEY_CLASSES_ROOT\Excel.Sheet.8\shell\Open\command should look like this: (Default) REG_SZ "C:\Program Files (x86)\Microsoft Office\Office12\EXCEL.EXE" "%1
command REG_MULTI_SZ vUpAVX!!!!!!!!!MKKSkEXCELFiles>tW{~$4Q]c@II=l2xaTO5 "%1"
Do the same for Excel.Sheet.12 Now Both .xls and .xlsx should open in new windows with no errors.
I have confirmed that the same problem occurs in Office 2010x64 (32bit probably also) when checking the dde option. This should fix All vista and windows 7 problems with opening excel in seperate windows
Enjoy!
geht auch, 