Keywords: VB6 | MSCOMCTL.OCX | Version Compatibility | Project File Modification | ActiveX Controls
Abstract: This paper provides a comprehensive analysis of the MSCOMCTL.OCX loading failure issue in VB6 IDE following Windows security update KB2687323. It examines the root cause of version compatibility problems in project files and presents practical solutions including modifying control version information in VBP files and removing NoControlUpgrade flags. The article also discusses supplementary approaches such as registry repair and system-level fixes, offering VB6 developers a complete troubleshooting guide.
Problem Background and Symptom Analysis
After installing Windows security update KB2687323, many Visual Basic 6.0 developers encountered issues where the IDE failed to load the MSCOMCTL.OCX control. The error message displayed as "'[project_vbp_path]/MSCOMCTL.OCX' could not be loaded--Continue Loading Project?" Notably, the path shown in the error message refers to the project file (.vbp) folder path rather than the control's actual registered system path.
This phenomenon exhibits the following typical characteristics: the MSCOMCTL.OCX control is properly registered in the system32 folder; executables compiled before the update run correctly and load the updated OCX control; the "Upgrade ActiveX Controls" checkbox in project properties fails to resolve the issue regardless of its setting.
Root Cause Investigation
Through in-depth analysis of project files, the problem was traced to version information definitions in VBP project files. A typical project file contains the following line:
Object={831FDD16-0C5C-11D2-A9FC-0000F8754DA1}#2.0#0; MSCOMCTL.OCXThe version identifier "2.0" becomes the critical factor preventing control loading. Security update KB2687323 provides a new fixed version of MSCOMCTL.OCX, but VB6 IDE cannot automatically upgrade the version reference from 2.0 to 2.1 in the project, resulting in version mismatch errors.
Core Solution
The most direct and effective solution is to manually modify the version information in the project file:
Object={831FDD16-0C5C-11D2-A9FC-0000F8754DA1}#2.1#0; MSCOMCTL.OCXThe specific operational steps are: open the .vbp project file using a text editor (such as Notepad); locate the line containing the MSCOMCTL.OCX reference; change the version identifier from "2.0" to "2.1"; save the file and reopen the project in VB6 IDE.
An even simpler method involves removing the flag that prevents automatic upgrades. In the VBP file, find and delete the following line:
NoControlUpgrade=1This setting prevents VB6 IDE from automatically upgrading control versions. Removing it allows the system to properly handle version compatibility issues.
Alternative Diagnostic Methods
When uncertain about the correct version information, create a new VB6 test project, add the MSCOMCTL control to a form, then examine the generated VBP file to see the version identifier expected by the system. This approach is particularly useful for handling loading failures of other OCX controls.
Supplementary Repair Solutions
Beyond modifying project files, system-level repair measures can be considered. Run the command prompt with elevated privileges and execute the type library registration command:
cd C:\Windows\System32\
regtlib msdatsrc.tlbOr for 64-bit systems:
cd C:\Windows\SysWOW64\
regtlib msdatsrc.tlbFor more complex registry corruption scenarios, batch files can be created for system repair. However, this method carries higher risks and should be performed under professional guidance.
Preventive Measures and Best Practices
To prevent similar issues from recurring, developers are advised to: regularly back up project files; test project compatibility before applying system updates; maintain development environment stability; understand version dependencies of third-party controls used.
By understanding VB6 project file structure and version management mechanisms, developers can better handle various compatibility issues and ensure long-term project maintainability.