What parameter are you estimating? Post your code. There might be something we can suggest
Many SAS procedures ensure that confidence intervals make sense for the parameter. For example, if you use PROC FREQ to estimate a binomial proportion, the CI for the proportion is always a subinterval of [0,1]. Similarly, a confidence interval for a variance or an odds ratio will never include a negative value.
If your statistic is assumed to be normally distributed, SAS will carry out the usual computations. SAS does not know when a parameter is bounded unless you tell it.
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