java.lang.NullPointerException error


I have beginner question.
I am using Test Suide with some exteral excel files, my test suide was working fine untli i change some data in the excel files.

Now when I try to start the testu suite i got error message:

at com.kms.katalon.core.testdata.reader.SheetPOI.getRowNumbers(
at com.kms.katalon.execution.entity.TestSuiteExecutedEntity.findTestData(
at com.kms.katalon.execution.entity.TestSuiteExecutedEntity.prepareTestCaseExecutedEntity(
at com.kms.katalon.execution.entity.TestSuiteExecutedEntity.loadTestCases(
at com.kms.katalon.execution.entity.TestSuiteExecutedEntity.prepareTestCases(
at com.kms.katalon.composer.execution.handlers.AbstractExecutionHandler$

Can someone explain where to look for solution ?

Not enough information you provided. Have a look at the following guideline.