I am using Stata14 to run RDD. When computing the optimal bandwidth using 'rdbwselect' I get the following error:

Invertibility problem in the computation of preliminary bandwidth below the thresholdInvertibility problem in the computation of bias bandw
> idth (b) below the thresholdInvertibility problem in the computation of bias bandwidth (b) above the thresholdInvertibility problem in th
> e computation of loc. poly. bandwidth (h) below the thresholdInvertibility problem in the computation of loc. poly. bandwidth (h) above t
> he threshold
Can anyone provide me with a solution or provide some insight as to why this might be occurring? The 'rdbwselect' command works fine when using example datasets so I do not believe it's associated with the version of stata I am using. The command I am using is:

Code:
rdbwselect ln_price rank if zone_1==1, c(90) p(1) kernel(triangular) bwselect(mserd) scaleregul(1)