According to Me Yes you can pursue the company secretary course along with the MBA course.Legally it's possible to do both course But one thing I Bring to your Notice is that MBA and as well as CS both are very vast courses, OK, to excel in the
course you need to put your full concentration in the each subject and need a thorough reference of various books and material throughout the course period without getting tired.

And also you MBA program demands your 100% devotion during the learning time of 2 years (which I feel the time becomes short for one to attain the knowledge
hidden in volumes of books) and you also required to attend various conferences and meet professionals etc

As per My Oprion is Not Good to do two major courses like MBA and CS.

Company Secretary is an professional degree which is organised by the ICSI.
The CS course has three stages which is Foundation programme, executive programme and professional programme.
Since you have completed the graduation, then you are exempted from the foundation programme and get direct entrance into executive programme.

So I Suggest you Either Do MBA or CS for both the Courses there Are the Entracne Test for MBA there is A Lot of the Entracne Exam like CAT, MAT, CMAT XAT Etc

for the CS you may go for the CS Foundation Exam

All the best