Generally speaking, in Wisconsin, the statute of limitations for a contract claim is 6 years. How that is interpreted however, can make a world of difference for your case.
The Wisconsin Courts have held that the six year statute of limitations for Breach of Contract claim is an absolute six years, running from the date of the breach, not when it is discovered.
The Court said in Williams v. Kaerek Builders, Inc. 212 Wis.2d 150, 568 N.W.2d 313 Wis.App.,1997 that
[Plaintiffs] were required to bring their breach of contract action within six years of the breach, regardless of whether they had knowledge of the breach or could have diligently discovered the breach. See CLL Assocs. Ltd. Partnership v. Arrowhead Pacific Corp., 174 Wis.2d 604, 617, 497 N.W.2d 115, 120 (1993).
What does this mean for your business and its possible lawsuits? It means that if there is any possibility of a claim, you need to bring them to an attorney right away. While you may think you have time, it may turn out that the breach occurred much earlier than you realize, and then your claim may be barred. Every case is different, and it is impossible to predict over the phone how the statute of limitations will apply in every case. Be sure to bring your matter right away to an attorney and inform them if you think there is any possibility that the breach took place at some point in the past.