Now to your question could be anything did you change anything before this happened >ocx files are ActiveX compnents and some are ok and some arnt some are maleware so it could be your antivirus removed some component of a maleware program and now when windows loads its looking for it but its hard to tell what it really is for.
If the file is on your computer, in the Windows\system32-directory I think, enter this at the commandline (Start>Run): regsvr32.exe actskn43.ocx
This should at least register it correctly
If that dont work try unisntalling and/or re-install any programs recently that may have generated this error. If this does not resolve your issue or you have not installed any program recently try recovering Windows back to a recent backup of Windows
Well try that and get back to me but pleas no yelling