When an application requires ac1st21.dll, Windows will check the application and system folders for this .dll file. If the file is missing you may receive an error and the application may not function properly.
.DLL Error Examples
This application has failed to start because ac1st21.dll was not found. Re-installing the application may fix this problem.
ac1st21.dll Not Found.
Possible fixes for ac1st21.dll errors.
Re-Install the application that requires ac1st21.dll.
Update the application to the latest version.
Install all Windows updates and any available driver updates.
Clean your registry and optimize your computer.
Download and install ac1st21.dll.
Did you know? You may already have this file even though you are getting .dll errors. That's because the .dll file may have been moved or renamed by another application.
Check to see if you already have ac1st21.dll on your computer.
For more information see how to search your PC for .dll files.