You tell me? Were you there? Did you enter the signed amendment as an exhibit with the lease? The judge seems to be declaring that there is a legitimate issue of dispute. That is why a trial is necessary. I urge you to get legal assistance.
Remember the issue in an eviction is possession of the unit, not the amount owed. the date of payment is the issue as well as whether the rent was paid. You should file a separate suit for what they owe you and any damages.
In Colorado unless one party defaults (or admits liability in open court) on the first appearance, the court has to set the matter for trial. The first hearing on an FED is not a trial, and the court doesn't take evidence. Here the tenant has a rational story, and even if you have other documents there is a factual dispute as to what and when the rent is owed. You should set the trial, and then come to trial with your documents, including copies of the cancelled checks received.
In this economy, however, you must understand that judges are loath to evict tenants unless the tenant is really behind and just won't or can't bring the rent up. Here it sounds like you are disputing over one months' rent. In an FED (Forcible Entry and Detainer action, which is the legal term for an eviction) you also have to remember that all the client has to do to stay in the house is show up at trial and pay you what you claim is late. The tenant always has the right to cure a non-monetary default.
Also in this economy, a tenant is a tenant. There are lots of landlords looking for tenants, so perhaps contacting your city or county mediation service (they run the program to help citizens in the community resolve disputes) could iron out the issues and allow you to keep a paying tenant.
Some attorneys sell unbundled legal services where you pay for just what you need and can afford. For example, some attorneys will give you an hour or two at a set price to review your issue and give you advice based on the law, prepare letters for you to sign, or sell the paperwork for the court filings; then you can proceed on your own, but knowing that your paperwork is correct.
Good luck. jim
NOTICE— The Legal Information contained in this answer is provided solely for informational purposes to assist the layman with understanding legal issues, and is not legal advice nor intended to create an attorney-client relationship between you and me or my law firm. Such Legal Information is intended for general informational purposes only and should be used only as a starting point for addressing your legal issues. It is not a substitute for an in-person or telephone consultation with an attorney licensed to practice in your jurisdiction about your specific legal issue, and you may not rely upon such Legal Information. You understand that questions and answers or other postings to the Site are not confidential and are not subject to attorney-client privilege.