What steps can be taken to solve the error message "Can't find GSD_DgnCalc.dll" that appears while using General Section Designer (GSD)?

Try to reinstall VC++. Please refer to the path below.
C:\Program Files\MIDAS\midas Civil\VC++ 2012 Redistributable Package
If you are using 64bit OS, reinstall both vcredist_x64.exe and vcredist_x86.exe.
If you are using 32bit OS, reinatall only vcredist_x86.exe.
Also when you reinstall VC++, try as an administrator.