ORA-14266: data type or length of an index subpartitioning column may

I was getting this error while trying to alter the data type for a column. as per the error . but as per the cause /action for this error there were no indexes/partitions on this column .

was not sure what is going on so i just dropped all the indexes( few normal index and partioned bitmap indexes) for this table and then when i try to do the alter it went fine .