It's impossible to know what went wrong without knowing exactly what you did, but it could be that your rennet is old. You will see that everyone here recommends using liquid rennet, not the tablets as its easier to measure the small amounts needed. Liquid rennet comes in single and double strengths (and for all I know, more concentrated than that). The supplier will give you a guideline as to how much to use - my bottle of double strength calf rennet says 1.25ml to 10l. It seems to me that most recipes which don't specify the type of rennet are using single strength rennet, and you can use either vegetarian or calf. Having said that, as you go on you will find that you need to finesse the amount of rennet as it has different effects on different milks. Search the forum on 'flocculation' and you'll find lots of information on how to decide when to cut your curd, how long it should take, etc, etc.
I suggest you detail what you did and that will give us more clues as to how to help you.