On launch, GnuCash launched the druid "auto-created transactions
notification". Next was hit twice and the program livelocked with the
following message repeated in the terminal:

Error: create_each_transaction_he...(): Null kvp_val for account
Error: create_each_transaction_he...(): Unable to find common
currency/commodity.

The problem was traced to this entry in the gnucash file:

5980,6022d6571
<       <gnc:transaction version='2.0.0'>
<         <trn:id type='guid'>90cedfbad8ab315cc70696dc4f69b030</trn:id>
<         <trn:currency>
<           <cmdty:space>ISO4217</cmdty:space>
<           <cmdty:id>GBP</cmdty:id>
<         </trn:currency>
<         <trn:date-posted>
<           <ts:date>1970-01-01 01:00:00 +0100</ts:date>
<         </trn:date-posted>
<         <trn:date-entered>
<           <ts:date>2003-08-23 17:27:29 +0100</ts:date>
<           <ts:ns>793570000</ts:ns>
<         </trn:date-entered>
<         <trn:description></trn:description>
<         <trn:splits>
<           <trn:split>
<             <split:id type='guid'>c3ed08ac14f93af125b342a6684e9a05</split:id>
<             <split:reconciled-state>n</split:reconciled-state>
<             <split:value>0/100</split:value>
<             <split:quantity>-1/0</split:quantity>
<             <split:account
type='guid'>711c30a132c5fab447d0eef4db3740ba</split:account>
<             <split:slots>
<               <slot>
<                 <slot:key>sched-xaction</slot:key>
<                 <slot:value type='frame'>
<                   <slot>
<                     <slot:key>credit-formula</slot:key>
<                     <slot:value type='string'>0.00</slot:value>
<                   </slot>
<                   <slot>
<                     <slot:key>debit-formula</slot:key>
<                     <slot:value type='string'></slot:value>
<                   </slot>
<                   <slot>
<                     <slot:key>account</slot:key>
<                     <slot:value
type='guid'>00000000000000000000000000000000</slot:value>
<                   </slot>
<                 </slot:value>
<               </slot>
<             </split:slots>
<           </trn:split>
<         </trn:splits>
<       </gnc:transaction>

Removing that entry fixed the problem. I have no idea what created it.