Please note that the error message could vary. Some of the common cases are: missing, corrupted, crashed, not found etc.
ext-ms-win-ntuser-windowclass-l1-1-1.dll is a DLL file part of ApiSet Stub DLL program which is developed by Microsoft. In order for the program to work properly, it needs a properly working dll file.
If you have visited this page and looking for the ext-ms-win-ntuser-windowclass-l1-1-1.dll file, you have mostl likely encountered one of the following errors below:
In order to fix the ext-ms-win-ntuser-windowclass-l1-1-1.dll error, you will need to download and install the DLL file in the appropriate directory. First, look at the download section on this page and get the corresponding version to your operating system. Pay close attention to the architecture of the file (either 32 or 64 bit), but also look for the language version. If there are multiple versions available we recommend you go with the latest one available.
Once you have downloaded the ext-ms-win-ntuser-windowclass-l1-1-1.dll file, make sure you extract it using WinRar or a similar tool and place it in the directory where the faulty program is located. If this doesn't solve your problem, you may also want to copy the downloaded ext-ms-win-ntuser-windowclass-l1-1-1.dll file in your System32 folder for 32Bit systems or SysWoW64 folder for 64bit based OS.