The Microsoft Terminal Services Client ActiveX control (also known as Microsoft RDP Client Control) is either not available, or is not enabled. For more information about installing and enabling this ActiveX control, see the Microsoft TechNet Web stie (http://go.microsoft.com/fwlink/?LinkId=103719).
The installation of Windows XP SP3 has disabled this ActiveX control.
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To Resolve:
open Internet Explorer
click Tools -> manage Add-ons -> enable/disable add-ons
Show: add-ons currently loaded in Internet Explorer
If Microsoft RD Client shows listed as disabled, click it and click enabled.
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If the controls are not displayed in the Manage Add-ons dialog box,
Open Regedit
Navigate to :
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Ext\Settings\
right-click {7584C670-2274-4EFB-B00B-D6AABA6D3850}, and then click Delete.
Close and restart Internet Explorer, and then try to connect to the computer by using Remote Web Workplace again. If you still get a message that says, “The Microsoft Terminal Services Client ActiveX Control (also known as Microsoft RDP Client Control) is unavailable,” proceed to step 5 to re-register the mstscax.dll file.
Click Start, click Run, in the Open box type %windir%\system32\regsvr32 mstscax.dll (see Figure 16), and then click OK.
close Internet Explorer and then re-launch it, go back to the manage add-ons as listed above.
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Add the Remote Web Workplace Web site you are trying to access to the trusted site list in Internet Explorer
Click Tools, and then click Internet Options.
In Internet Options, click Security.
On the Security tab, click Trusted sites, and then click Sites.
In Trusted sites, for Add this website to the zone, type your organization’s Web address (URL) for Remote Web Workplace, for example, https://remote.website.com.
Click Add
click Close.