Hi,
In the roadmap code for bPlusCreate, it is not specified to setAttrCatEntry after creating a new root block. Because of this, when we call bPlusInsert, it is checked whether attrCatEntry has a rootblock and E_NOINDEX is returned. Therefore, when we create an index and then drop it, the error message of NO INDEX is seen.
TL;DR
In bPlusInsert this line:
int blockNum = /* rootBlock of B+ Tree (from attrCatEntry) */;
results in blockNum getting value -1 as we had not set AttrCatEntry with rootBlock in bPlusCreate function.