Try this if you are still having this problem.
try to find the file Preferences.xml (path for Inventor 2011 as below) and open it using notepad.
C:\Documents and Settings\<user name>\Application Data\Autodesk\Autodesk Inventor 2011\Objects\Preferences.xml
C:\Users\<user name>\AppData\Roaming\Autodesk\Autodesk Inventor 2011\Objects\Preferences.xml
Then you should be able to find the content as below, and make sure the value of property “Suppressed” is “False”.
<Category>
<Property Value="True" />
<Property Name="Suppressed" Value="False" />
<Property Name="CreateDWFAttachmentApplyToAllFiles" Value="True" />
<Property Name="DeleteWorkingCopy" Value="False" />
<Property Name="IncludeParents" Value="False" />
<Property Name="KeepFilesCheckedOut" Value="False" />
<Property Name="CreateDWFAttachment" Value="False" />
<Property Name="DirectParentsOnly" Value="False" />
<Property Name="SendToJobServer" Value="False" />
</Category>
If you can’t find the content in the file, you could try to delete the file and restart Inventor. It should be re-generated automatically.