A violation of probation is a serious problem. These are difficult to beat and often show that you are dealing with a zealous prosecutor, or prosecutor's office.
A violation of probation (VOP) is basically a "breach of contract" case. Many prosecutors love doing these since this is even more like shooting fish in a barrel than their usual cases. That is because they only need to prove that you violated your probation by a "preponderance of the evidence."
This means that they only need to prove that you violated the conditions of your probation by 51%. So if the judge (you don't get a jury for a VOP) believes that it is more than likely that you violated your probation, than you are guilty of this violation.
This standard is much lower than the standard needed to prove you guilty of the substantive offense in front of a jury - that standard is "beyond a reasonable doubt."
If you are dealing with a VOP on a misdemeanor case, the consequences are not that great, since you cannot get more than a year in jail - and most likely it may only be a matter of weeks or in a worst case scenario a matter of months.
However, a felony VOP is very serious, since you may be facing prison time even when you only did time in the county jail on the underlying offense.
For all the reasons above, it is absolutely imperative that you consult with a knowledgable criminal defense attorney if you are charged with a felony VOP.
Obligatory disclaimer: nothing in the statements above are meant to imply an attorney-client relationship.