用hlm处理数据 没有结果 而出现这样一段话：There is a problem in the fixed portion of the model.  A near singularity islikely.  Possible sources are a collinearity or multicollinearity among the
predictors.  We suggest that you examine a correlation matrix among the fixed
effect predictors.
不明白这是什么意思啊？问题出在哪了？请大家指点。