Hey guys.
I am - again - irregularly experiencing troubles, that I suddenly cannot close won opportunities. 

The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 30124000000LrED . Flow error messages: <b>An unhandled fault has occurred in this flow</b><br>An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.

The Salesforce Email (below) mentions an error "Pricebook2Id__NotFound" - I'm not sure what this means. The pricebooks are all in place and working - The strangest thing is that this error happens every few days then suddenly everything goes normal again.

I tried to work with Mayank Srivastava's solution from this post: https://success.salesforce.com/answers?id=9063A0000019NR7QAM
However my Flow designer is completely blank - I cannot see any unsaved flows.

Any suggestions what I can do?
Much appreciated!



Here is the Error-Email Salesforce send to me 


Error element myRule_1_A1 (FlowRecordCreate).
This error occurred when the flow tried to create one or more records: Error occurred attempting to get data type for : RawFieldImpl[tableName: Order, columnName: Pricebook2Id__NotFound]. For details, see API Exceptions.

This report lists the elements that the flow interview executed. The report is a beta feature.
We welcome your feedback on IdeaExchange.

Flow Details
Flow Name: Opportunity_Won
Type: Workflow
Version: 22
Status: Active

Flow Interview Details
Interview Label: 
Current User: Clemens Kemper (00524000001SVfn)
Start time: 30.10.2017 11:56
Duration: 0 seconds

How the Interview Started
Clemens Kemper (00524000001SVfn) started the flow interview.
Some of this flow's variables were set when the interview started.
myVariable_old = 0062400000ZuIsPAAV
myVariable_current = 0062400000ZuIsPAAV

ASSIGNMENT: myVariable_waitStartTimeAssignment
{!myVariable_waitStartTimeVariable} Equals {!Flow.CurrentDateTime}
Result
{!myVariable_waitStartTimeVariable} = "30.10.2017 11:56"

DECISION: myDecision
Executed this outcome: myRule_1
Outcome conditions: and
1. {!myVariable_current.IsWon} (true) Equals true
Logic: All conditions must be true (AND)

DECISION: myRule_1_pmetdec

RECORD CREATE: myRule_1_A1
Create one Order record where:
AccountId = {!myVariable_current.AccountId} (0012400001NmjFxAAJ)
Ansprechpartner__c = {!myVariable_current.Ansprechpartner__c} (null)
Auf_Wasser__c = {!myVariable_current.Auf_Wasser__c} (false)
BillingCity = {!myVariable_current.Account.BillingCity} (Kempen)
BillingCountry = {!myVariable_current.Account.BillingCountry} (null)
BillingPostalCode = {!myVariable_current.Account.BillingPostalCode} (47906)
BillingStreet = {!myVariable_current.Account.BillingStreet} (Wiesenstraße 66)
EffectiveDate = {!myVariable_current.CloseDate} (30. October 2017)
Opportunity__c = {!myVariable_current.Id} (0062400000ZuIsPAAV)
Pricebook2Id__NotFound = {!myVariable_current.Pricebook2.Id} (01s24000004FUmIAAW)
Rechnungsdatum__c = {!myVariable_current.CloseDate} (30. October 2017)
Status = Draft
Veranstaltungsart__c = {!myVariable_current.Veranstaltungsart__c} (null)
Z_nddatum__c = {!myVariable_current.Z_nddatum__c} (18. August 2018)
Z_ndzeit__c = {!myVariable_current.Z_ndzeit__c} (null)
berraschung_f_r__c = {!myVariable_current.berraschung_f_r__c} (null)
ueberraschung__c = {!myVariable_current.berraschung__c} (false)
Result
Failed to create record.

Error Occurred: Error occurred attempting to get data type for : RawFieldImpl[tableName: Order, columnName: Pricebook2Id__NotFound]