Same problem here.
Any solution yet? Rebuilded rpmdb already. Did a zypper clean as well. Zypper update seem to work though. However, no change to install anything from the store nor the most recent update (.27).
Thanks!

EDIT:
pkmon output for a failed transaction:
[root@Jolla rpm]# pkmon -v
18:26:10 PackageKit Verbose debugging enabled (on console 1)
18:26:10 PackageKit refreshing task list
Transactions:
[none]
18:26:10 PackageKit notify::connected
daemon connected=1
18:26:10 PackageKit refreshing task list
network status=online
Daemon state: 'State:
'
18:26:15 PackageKit emit transaction-list-changed
18:26:15 PackageKit current: /55869_ebddadee
18:26:15 PackageKit emit added: /55869_ebddadee
18:26:15 PackageKit added: /55869_ebddadee
Transactions:
1 /55869_ebddadee
Daemon state: 'State:
0 refresh-cache /55869_ebddadee state[running] exclusive[1] background[0]
'
/55869_ebddadee allow_cancel 1
/55869_ebddadee percentage -1
18:26:15 PackageKit role now refresh-cache
/55869_ebddadee role refresh-cache
/55869_ebddadee status setup
/55869_ebddadee status finished
18:26:15 PackageKit emit transaction-list-changed
18:26:15 PackageKit last: /55869_ebddadee
18:26:15 PackageKit emit removed: /55869_ebddadee
18:26:15 PackageKit removed: /55869_ebddadee
Transactions:
[none]
18:26:15 PackageKit failed to adopt: Could not configure normal mode.
Daemon state: 'State:
0 refresh-cache /55869_ebddadee state[finished] exclusive[1] background[0]
'



and another try:

18:25:34 PackageKit Verbose debugging enabled (on console 1)
18:25:34 PackageKit refreshing task list
Transactions:
[none]
18:25:34 PackageKit notify::connected
daemon connected=1
18:25:34 PackageKit refreshing task list
network status=online
Daemon state: 'State:
'
18:25:38 PackageKit emit transaction-list-changed
18:25:38 PackageKit current: /55868_cbaddede
18:25:38 PackageKit emit added: /55868_cbaddede
18:25:38 PackageKit added: /55868_cbaddede
Transactions:
1 /55868_cbaddede
Daemon state: 'State:
0 refresh-cache /55868_cbaddede state[running] exclusive[1] background[0]
'
/55868_cbaddede percentage -1
18:25:38 PackageKit role now refresh-cache
/55868_cbaddede role refresh-cache
/55868_cbaddede status finished
18:25:38 PackageKit internal error: failed, but no exit code: failed
18:25:38 PackageKit failed to adopt: Failed: failed
18:25:38 PackageKit emit transaction-list-changed
18:25:38 PackageKit last: /55868_cbaddede
18:25:38 PackageKit emit removed: /55868_cbaddede
18:25:38 PackageKit removed: /55868_cbaddede
Transactions:
[none]
Daemon state: 'State:
0 refresh-cache /55868_cbaddede state[finished] exclusive[1] background[0]
'