You have opened at least one secured db on your machine, or someone has, which has changed the default workgroup. Using explorer look for all files *.mdw. If you find any other than system.mdw then find the file Wrkgadm.exe. Double click on this file then select Join and point to the system.mdw file in the system32 directory.
If you don't find any other .mdw files named other than system.mdw, delete the system.mdw file in the system32 directory. Now double click on the Wrkgadm.exe file. Select Create New, name it system.mdw and store it in the system32 directory. If it ask do not assign the Admin a password. Now you should be good to go.
Or an alternative to the second option is go to the other machine not having problems if it has the same Windows version and Access version and copy the system.mdw file from the system32 directory and replace the one on your troubled pc.
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