RSLinx -102: OS/Driver Mismatch, Not a PLC-5 Fault

The panel shows PCL-Link-Error returned an error code of -102, followed by Who-NT - Unable to load virtual device driver. AI-5 then cannot reach the PLC-5/25 through the RSLinx path. Start with the PC software stack: the fault occurs while AI-5 loads its communications interface, before a PLC response is possible.

Stop applying fixes that cannot clear -102

Engineers usually change the PLC route, reinstall the programming package, or start building the Excel DDE link. Those actions miss the failed layer.

• Do not change PLC-5 logic or addresses. Error -102 occurs before AI-5 can exchange application data with the controller.
• Do not troubleshoot DDE first. Excel cannot read PLC words until AI-5 and RSLinx can use the underlying driver.
• Do not keep renaming the same RSLinx driver. A wrong server name can break routing, but it does not repair a virtual device driver that the operating system cannot load.
• Do not expect an AI-5 update alone to solve it. Updating from AI-5 8.05 to 8.07 on Windows 98 did not clear the error with RSLinx Professional 2.42.
• Do not run the NT driver-selection utility on Windows 98. That selects the wrong host interface for the operating system.

Read the symptoms as a host-driver failure

AI-5 is a legacy application that calls RSLinx through an operating-system-specific bridge. Windows 95/98 and Windows NT/2000/XP require different selections. If the bridge cannot load, neither the configured RSLinx driver nor the 1784-KF2/B path gets a chance to communicate.

Choose a stack that matches the operating system

The failed combination was Windows 98, AI-5 8.07, and RSLinx Professional 2.42. On that computer, replacing Professional 2.42 with RSLinx Lite 1.70.62 restored AI-5 communications. That test isolates a software compatibility problem, but Lite does not satisfy the stated DDE requirement.

Use one of these decision paths:

• If Windows 98 must remain: select the AI-5 Windows 95/98 interface and use a RSLinx generation that actually communicates with that installation. Test the licensed edition required for DDE before building the workbook.
• If RSLinx Professional 2.42 and DDE must remain: move the installation to Windows 2000 or Windows XP, then select the NT/2000/XP AI-5 interface. AI-5 8.07 was the version used for this route.
• If AI-5 8.05 must remain: treat its operating-system compatibility as a separate constraint. Do not infer compatibility from the behavior of 8.07.

The first check is always the operating system versus the interface selected by Markexe.exe. Driver names and DDE topics come later.

Rebuild the communications path in order

1. Record the installed versions. Note the Windows release, AI-5 version, RSLinx edition and version, selected communications hardware, configured RSLinx driver name, and the complete error text.
2. Select the correct AI-5 interface. On Windows 98, run Markexe.exe 95 from the AI-5 folder, or reinstall AI-5 to restore RSLinx Driver under Win95/98. Do not run Markexe.exe NT on that host. On Windows NT, Windows 2000, or Windows XP, run Markexe.exe NT so AI-5 offers the NT-family RSLinx driver.
3. Configure the physical driver in RSLinx. Set the driver for the actual connection through the 1784-KF2/B. Confirm that RSLinx can browse the PLC-5/25 before opening AI-5.
4. Match the AI-5 server name exactly. Enter the configured RSLinx driver name in the AI-5 RSLinx Driver Default Server Name field. For example, if RSLinx names the driver AB_DF1-1, AI-5 must use AB_DF1-1 with the same punctuation.
5. Open AI-5 and test controller access. Clear the programming-software communication fault before configuring Excel.
6. Configure DDE in RSLinx Professional. Create the DDE topic against the verified PLC path, then request only the required PLC words. Obtain the exact Excel link syntax from the installed RSLinx DDE documentation because it depends on the configured topic and data address.

Verify each layer before moving forward

• Host layer: AI-5 opens without -102 or the Who-NT virtual-device message.
• RSLinx layer: the configured driver browses to the intended PLC-5/25 through the 1784-KF2/B.
• AI-5 layer: AI-5 uses the exact RSLinx driver name and can perform an online operation without losing communications.
• DDE layer: RSLinx Professional resolves the configured topic and returns a known PLC word to Excel.
• Data check: change a safe test word through the normal control process and confirm that Excel follows the value. A static number proves only that a link returned data once.

If RSLinx browses the controller but AI-5 still reports -102, stay at the host integration layer. Changing the KF2 route, PLC address, or Excel formula wastes time because those layers have not been reached.

Avoid the recurring legacy-system traps

Running Markexe.exe NT on Windows 98 can leave AI-5 pointed at the wrong virtual driver. Reverse it with Markexe.exe 95 or reinstall AI-5; selecting the Windows 95/98 option in a dialog is not enough if the executable was previously marked for the NT interface.

A successful connection with Lite 1.70.62 proves that an older stack can reach the controller. It does not prove that Professional 2.42 can supply DDE on the same Windows 98 installation. Test communications again after every edition or version change.

When AB5.exe disappears on Windows XP, launch it from a command prompt so the console remains open and preserves the startup error. Windowed mode, font changes, and compatibility settings can improve display behavior, but they do not correct a communications virtual-driver failure.

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