The 11.0.07 update delivers 64-bit support via separate 32-bit and 64-bit DLLs, and the implementation follows Microsoft's guidelines. Because VB 6.x offers no 64-bit support, applications built with the VB6 environment no longer work.

Workarounds

The following options are available:

• Update to a newer IDE or later version of Visual Basic that supports 64-bit DLLs.
  
• If you had previously built applications as 32 bit because the AcroPDF.dll was 32 bit and are using Visual Studio 2005 or later, verify that your Visual Studio Platform Target setting is Any CPU (the default). Any CPU means that the assembly runs natively on the CPU is it currently running on. That is, as 64 bit on a 64-bit machine and 32 bit on a 32-bit machine. 
  
• If you control the end-user environment, do not update machines to 11.0.07 until you have rebuilt your application with the correct settings.
• Build your application so that the web browser controls the loading of the Acrobat or Reader plug-in rather than calling the DLL directly. For some ideas, see the forum thread.

Additional information

The software world is rapidly moving to 64-bit applications, and it is becoming more common to encounter scenarios where 64-bit plug-ins and support are required. Note the following:

• Acrobat 11.x products only support Visual Studio 2008 SP1 and later.
• Since Acrobat 9.x, Visual Studio 2005 or later has been required.
• Microsoft end-of- lifed the Visual Basic 6.0 IDE as of April 8 2008.
  
• Microsoft never offered 64-bit support with Visual Basic 6.0. From their website: "The Visual Basic 6.0 IDE has never been offered in a native 64-bit version, nor has the 32-bit IDE been supported on 64-bit Windows. VB6 development on 64-bit Windows or any native architecture other than 32-bit is not and will not be supported."