Please ignore it. Now it is working. There was some Windows security issues.
I have downlaoded standard Process Book Add-in .NET VB template from vCampus and successfully build through Visual Studio 2005. I have registered the Add-in in Windows Registry by running the standard AddinReg.reg file from the template. I also copied the DLL files (say AddinPBToolBar_VB1.DLL and *.TLB file) in PIPC\ProcBook folder. I have added following one line (in bold) to open a PB Schematic in the basic OSISoft template in the OnConnection function.
On Error GoTo error_handler
m_App = CType(application, PBObjLib.Application)
'Region: Command Bar
Now whenever I tried to add this add-in from Menu->Tools->Add-in Manager, it shows my add-in "VB Toolbar Add-in Template" and when I select Loaded and press OK, Process Books throws Error: "VB Toolbar Addin Template" could not be loaded.
I have same problem with all other standard PB add-in template (AddinPBSimple_VB1, AddinPBDockWin_VB1, AddinPBIDP3_BV1). So basically it looks like my Process Book 3.1 is unable to load the Add-in. Has anyone face similar problem or can provide some assisstance. Thanks.