On connecting the USB to the host Device is detected and in Device Manager it shows “Microsoft USB Sync” type device.The DefaultClientDriver in Register for above case is “Serial_Class”.  When we change the DefaultClientDriver to “USBSER_Class”, after connecting with host it shows “Generic Serial” under the other devices in Device manager. Actually I want to connect device (WM 6.0) with windows XP through Active sync I don’t know which Register Entry I required out of (Serial_Class / USBSER_Class). I tried to connect with active sync 4.5 with both registry settings but it did not detect any device. Please guide me where I am missing or wrong. The registry setting which we are using is giving at the end of mail.  [HKEY_LOCAL_MACHINE\Drivers\BuiltIn\USBFN]    "InterfaceType"=dword:0     ; Internal    "Prefix"="UFN"    "Dll"="usbfn.dll"    "Order"=dword:2    "Priority256"=dword:64    "MemBase"=dword:40600000   ; UDC_BASE_U_VIRTUAL    "MemLen"=dword:1000        ; Needs at least 0xE04. Round up to 1 page.    "Sysintr"=dword:1a    "BusIoctl"=dword:2a0048    "IClass"=multi_sz:"{E2BDC372-598F-4619-BC50-54B3F7848D35}=%b","{6F40791D-300E-44E4-BC38-E0E63CA8375C}=%b"    "ForceFullSpeed"=dword:1        [HKEY_LOCAL_MACHINE\Drivers\USB\FunctionDrivers]   "DefaultClientDriver"=- ; erase previous default [HKEY_LOCAL_MACHINE\Drivers\USB\FunctionDrivers]   "DefaultClientDriver"=" Serial_Class" [HKEY_LOCAL_MACHINE\Drivers\USB\FunctionDrivers\Serial_Class]   "Dll"="serialusbfn.dll"   "DeviceName"="USBFNS1:"   "Prefix"="COM"   "DeviceArrayIndex"=dword:0   "RxBufferSize"=dword:4000   "IClass"="{CC5195AC-BA49-48a0-BE17-DF6D1B0173DD}"; idVendor must be changed. 045E belongs to Microsoft and is only to be used for; prototype devices in your labs. Visit http://www.usb.org to obtain a vendor id.   "idVendor"=dword:045E   "Manufacturer"="Generic Manufacturer (PROTOTYPE--Remember to change idVendor)"   "idProduct"=dword:00ce   "Product"="Generic Serial (PROTOTYPE--Remember to change idVendor)"   "bcdDevice"=dword:0   "Tsp"="Unimodem.dll"   "DeviceType"=dword:0 [HKEY_LOCAL_MACHINE\Drivers\USB\FunctionDrivers\USBSER_Class]   "Dll"="serialusbfn.dll"   "DeviceName"="USBFNS2:"   "Prefix"="COM"   "DeviceArrayIndex"=dword:0   "RxBufferSize"=dword:4000   "IClass"=multi_sz:"{CC5195AC-BA49-48a0-BE17-DF6D1B0173DD}","{C375C787-B721-4b8e-B67F-A112D5C0A404}"; idVendor must be changed. 045E belongs to Microsoft and is only to be used for; prototype devices in your labs. Visit http://www.usb.org to obtain a vendor id.   "idVendor"=dword:045E   "Manufacturer"="Generic Manufacturer (PROTOTYPE--Remember to change idVendor)"   "idProduct"=dword:0079   "Product"="Generic Serial (PROTOTYPE--Remember to change idVendor)"   "bcdDevice"=dword:90   "Tsp"="Unimodem.dll"   "DeviceType"=dword:0 [HKEY_LOCAL_MACHINE\Comm\USB\Linkage]    "Bind"=multi_sz:"USBFNSER1" [HKEY_LOCAL_MACHINE\Comm\USBFNSER]   "DisplayName"="USB Driver"   "Group"="Serial"   "ImagePath"="serialusbfn.dll" [HKEY_LOCAL_MACHINE\Comm\USBFNSER\Linkage]   "Route"=multi_sz:"USBFNSER1"      [HKEY_LOCAL_MACHINE\Comm\DefaultConnections]            "USBDefault"=multi_sz:"USB cable","115200"    ;Default Connect id    [HKEY_CURRENT_USER\ControlPanel\Comm]"AutoCnct"=dword:00000001"Cnct"="USBDefault" ENDIF BSP_NOSPI !