Here's a fix for the WSClient.dll error popup in Windows 10 build 11099

Almost a week ago on Wednesday, Microsoft rolled out Windows 10 build 11099 Insider Preview, also known as Redstone, on the Fast ring. And since then several people have reported a weird glitch when the build is booted up or restarted, which causes a popup window to display the error message "error in wsclient.dll Missing entry: RefreshBannedAppsList". This can be clicked away and you won't be bothered with it again, until you restart the OS. But here's a more permanent workaround.

@iCoreMastah370 I haven't seen that as a common issue. Please report in the Feedback app. Try running wsreset from CMD to fix
— Gabriel Aul (@GabeAul) January 15, 2016

Although Gabe Aul didn't acknowledge this to be a widespread issue, he did suggest a fix that appears to work for some and not for others. If you are getting the error popup, open a elevated command prompt and type wsreset, then hit enter, wait for 30-45 seconds until it completes by opening the Windows Store app.

Over on Reddit, a user looked into the issue a bit more, and discovered that:

the new WSClient.DLL in build 11099 exports 4 fewer functions than the one on earlier builds. The functions no longer exported are DllCanUnloadNow, DllGetClassObject, RefreshBannedAppsList and g_bPrintFromClientDLL. Deleting or disabling the task is the only way to have the error stop reappearing.

As you can probably guess, the task has to do with the Windows Store, and a change introduced with build 11099 is causing this error, although it isn't clear under which specific scenarios this affects people. If the above "wsreset" fix does not work for you and you want to avoid the popup error on each restart, do the following:

Hit Start/Cortana
Type Sch ...
Hit Task Scheduler
Tree down to Microsoft/Windows/WS
Right click on the task WSRefreshBannedAppsListTask
Click Disable

Pending an official acknowledgement of the issue from Microsoft, this will suppress the error popup until a newer build is released on the Fast ring. Users on Reddit have confirmed that the Store works normally and apps can still be installed with the task disabled, but you might want to bookmark this post or the Reddit thread to remind yourself to re-enable the task again once a newer build becomes available.

Via Reddit