I want to insert some records, however i am not able to insert the records. I am getting the exception:

11:13:27.559
(1559754000)|SYSTEM_METHOD_ENTRY|[57]|MAP>.containsKey(Object)
11:13:27.559
(1559819000)|EXCEPTION_THROWN|[EXTERNAL]|System.StringException:
Invalid id: 10356253

Please help what is going wrong. Here is my code.

trigger OrderHistory on Sales_Order__c (after insert)
{
    String s2 = String.valueOf(Trigger.New[0].Name);
    String s1 = s2.mid(2,8);

    List < OpportunityLineItem >  o1 = [Select Sales_Order__c, OpportunityId, ID_Opp_Product_18__c from OpportunityLineItem where Sales_Order__c in : s1];

    //Map with Key: Sales_Order__c and Value: List of OpportunityLineItem
    Map< ID, List< OpportunityLineItem >> map_records = new Map<  ID , List< OpportunityLineItem >>();
    List < OpportunityLineItem > tempo1 = new List< OpportunityLineItem >();

    for(OpportunityLineItem o : o1)
    {
        if(map_records.containsKey(o.Sales_Order__c))
        {
            tempo1 = map_records.get(o.Sales_Order__c);
            tempo1.add(o);
            map_records.put(o.Sales_Order__c , tempo1);
        }
        else
        {
            tempo1 = new List< OpportunityLineItem >();
            tempo1.add(o);
            map_records.put(o.Sales_Order__c , tempo1);
        }
    }

    List< OpportunityLineItem > o1TBU = new List< OpportunityLineItem >();
    for (Sales_Order__c so : Trigger.new)
    {
        String s3 = String.valueOf(so.Name);
        String s4 = s2.mid(2,8);
        if(map_records.containsKey(s4))
        {
            for(OpportunityLineItem o2 : map_records.get(s4))
            {
                if(o1!=null)
                {
                    o2.Order_History__c  = so.Id;
                    o1TBU.add(o2);
                }
            }
        }
    }

    update o1TBU;
}

Update

I tried using Map< String, List< OpportunityLineItem >> however it is giving that mapping cannot be done over string, it needs an id.
Secondly, yes sales_Order__c field isn't a lookup, so i tried using the OpportunityId field, but i am getting this in my debug logs:
1

4:48:08.776
(776937000)|SYSTEM_METHOD_ENTRY|[82]|MAP>.get(Object)
14:48:08.777
(777416000)|EXCEPTION_THROWN|[EXTERNAL]|System.StringException:
Invalid id: 10356253 14:48:08.777
(777603000)|SYSTEM_METHOD_EXIT|[82]|MAP>.get(Object)
14:48:08.777 (777724000)|FATAL_ERROR|System.StringException: Invalid
id: 10356253

Here is my updated code:

trigger OrderHistory on Sales_Order__c (after insert)
{

String s2 = String.valueOf(Trigger.New[0].Name);
String s1 = s2.mid(2,8);

List < OpportunityLineItem >  o1 = [Select Sales_Order__c,OpportunityId,ID_Opp_Product_18__c from OpportunityLineItem where Sales_Order__c  =: s1];
System.Debug (s1);
//Map with Key: Sales_Order__c and Value: List of OpportunityLineItem
Map<ID, List<OpportunityLineItem>> OpportunityLineItemRecord = new Map<ID, List<OpportunityLineItem>>();
List < OpportunityLineItem > tempo1 = new List< OpportunityLineItem >();

for(OpportunityLineItem o : o1)
{
   //System.Debug (o.Sales_Order__c);
    if(OpportunityLineItemRecord.containsKey(o.ID_Opp_Product_18__c))
    {
        tempo1 = OpportunityLineItemRecord.get(o.ID_Opp_Product_18__c);
        system.debug( tempo1);
        tempo1.add(o);
        OpportunityLineItemRecord.put(o.ID_Opp_Product_18__c , tempo1);
    }
    else
    {
        tempo1 = new List< OpportunityLineItem >();
        tempo1.add(o);
        OpportunityLineItemRecord.put(o.ID_Opp_Product_18__c , tempo1);
    }
}

List< OpportunityLineItem > o1TBU = new List< OpportunityLineItem >();
for (Sales_Order__c so : Trigger.new)
{
     String s3 = String.valueOf(so.Name);
     String s4 = s2.mid(2,8);

// if(OpportunityLineItemRecord.containsKey(so.id))
// {
for(OpportunityLineItem o2 : OpportunityLineItemRecord.get(s4))
{
if(o1!=null)
{
o2.Order_History__c = so.Id;
System.debug( o2.Order_History__c);
o1TBU.add(o2);
}
}
}
// }

update o1TBU;

}