The spring:form tag was added to the openmrs header in 1.7. See this line in include.jsp:
<%@ taglib prefix="form" uri="/WEB-INF/taglibs/spring-form.tld" %>
To use this in your module, set your config.xml to have a required openmrs version of at least 1.7 or greater.
FAQ
Question
How to fix this error?
/WEB-INF/view/module/growthchart/growthChartForm.jsp(3,72) Attempt to redefine the prefix form to http://www.springframework.org/tags/form, when it was already defined as /WEB-INF/taglibs/spring-form.tld in the current scope.
Solution #1:
If you want to retain backwards compatibility in your module, don't use "form" in your header, e.g. change to using this in your header: <%@ taglib prefix="springform" uri="/WEB-INF/taglibs/spring-form.tld" %>
and this: <springform:form ...> in your code.
Solution #2:
If you don't want to support OpenMRS 1.6 or below:
1) delete the taglib prefix in your header
2) Change your config.xml to have at least 1.7 in the require_openmrs_version element.