Gnucash 2.6.18 export to sqlite is failing

[bugzilla]

   Hi everyone,

   when I try to export my xml file to sqlite3 it fails with the following
   error message in gnucash.trace

   * 21:57:19  INFO <qof.object> [qof_object_foreach] type=gncTaxTable
   * 21:57:19  INFO <qof.engine> [qof_collection_foreach] Hash Table size
   of gncTaxTable before is 1
   * 21:57:19  CRIT <gnc.backend.dbi> [sqlite3_error_fn()] DBI error: 19:
   NOT NULL constraint failed: taxtable_entries.account
   * 21:57:19  CRIT <gnc.backend.dbi> [conn_execute_nonselect_statement()]
   Error executing SQL INSERT INTO
   taxtable_entries(taxtable,account,amount_num,amount_denom,type)
   VALUES('08f93e8d3586eaa430e8f3213c1d0e0b',NULL,12000000,100000,1)
   * 21:57:19  CRIT <gnc.backend.sql> [gnc_sql_do_db_operation()] SQL
   error: INSERT INTO
   taxtable_entries(taxtable,account,amount_num,amount_denom,type)
   VALUES('08f93e8d3586eaa430e8f3213c1d0e0b',NULL,12000000,100000,1)
   * 21:57:19  INFO <qof.engine> [qof_collection_foreach] Hash Table size
   of gncTaxTable after is 1
   * 21:57:19  INFO <qof.object> [qof_object_foreach] type=gncVendor

   If I search my xml file for the string 08f93e8d3586eaa430e8f3213c1d0e0b
   I will get entries which look like this:

   <gnc:GncEntry version="2.0.0">
     <entry:guid type="guid">07ec55f2b0c25d1fb9c6abc17e60e9bd</entry:guid>
     <entry:date>
       <ts:date>2014-08-08 12:00:00 +0200</ts:date>
     </entry:date>
     <entry:entered>
       <ts:date>2009-11-19 09:59:37 +0100</ts:date>
     </entry:entered>
     <entry:description>Invoice description</entry:description>
     <entry:qty>1000000/1000000</entry:qty>
     <entry:i-acct
   type="guid">8ca307f6b598a944c90b5a51e2ca59c4</entry:i-acct>
     <entry:i-price>10600000/1000000</entry:i-price>
     <entry:invoice
   type="guid">ee97b01eaa71273e88224d4082b75f5b</entry:invoice>
     <entry:i-disc-type>VALUE</entry:i-disc-type>
     <entry:i-disc-how>SAMETIME</entry:i-disc-how>
     <entry:i-taxable>0</entry:i-taxable>
     <entry:i-taxincluded>0</entry:i-taxincluded>
     <entry:i-taxtable
   type="guid">08f93e8d3586eaa430e8f3213c1d0e0b</entry:i-taxtable>
   </gnc:GncEntry>

   <gnc:GncTaxTable version="2.0.0">
     <taxtable:guid
   type="guid">08f93e8d3586eaa430e8f3213c1d0e0b</taxtable:guid>
     <taxtable:name>Steuertabelle 01</taxtable:name>
     <taxtable:refcount>0</taxtable:refcount>
     <taxtable:invisible>1</taxtable:invisible>
     <taxtable:parent
   type="guid">8e569076878f8126daafb6900ec07356</taxtable:parent>
     <taxtable:entries>
       <gnc:GncTaxTableEntry>
         <tte:amount>12000000/100000</tte:amount>
         <tte:type>VALUE</tte:type>
       </gnc:GncTaxTableEntry>
     </taxtable:entries>
   </gnc:GncTaxTable>
   <gnc:GncTaxTable version="2.0.0">
     <taxtable:guid
   type="guid">8e569076878f8126daafb6900ec07356</taxtable:guid>
     <taxtable:name>Steuertabelle 01</taxtable:name>
     <taxtable:refcount>0</taxtable:refcount>
     <taxtable:invisible>0</taxtable:invisible>
     <taxtable:child
   type="guid">08f93e8d3586eaa430e8f3213c1d0e0b</taxtable:child>
     <taxtable:entries>
       <gnc:GncTaxTableEntry>
         <tte:amount>12000000/100000</tte:amount>
         <tte:type>VALUE</tte:type>
       </gnc:GncTaxTableEntry>
     </taxtable:entries>
   </gnc:GncTaxTable>

   However if I set up a new file with some test entries exporting to
   sqlite3 is not a problem.

   Would appreciate any hint which narrows the root course of this
   problem.

   Thanks