Error: (incompatible character encodings: UTF-8 and ASCII-8BIT)

[Alexandros]

I have a Bibapp installation using
-ruby 1.9.3p0 (2011-10-30 revision 33570) [x86_64-linux]
-Rails 3.2.13

-java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)

and the attached Gems

Ι am trying to insert some Articles with Greek characters and after i do so, i get the following error:

Started GET "/el/works?view=all" for 192.168.0.25 at 2013-06-03 16:48:34 +0300
Processing by WorksController#index as HTML
Parameters: {"view"=>"all", "locale"=>"el"}

===Works: nil
(0.3ms) SELECT COUNT(*) FROM "people" WHERE "people"."active" = 't'
Search params: :, ["person_active:true", "status:3"], year_sort, descending, 0, , 10}
(0.4ms) SELECT COUNT(*) FROM "works"
User Load (0.4ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
Role Load (0.3ms) SELECT "roles".* FROM "roles" WHERE (name = 'admin' and authorizable_type = 'System' and authorizable_id IS NULL) LIMIT 1
Role Exists (0.3ms) SELECT 1 AS one FROM "roles" INNER JOIN "roles_users" ON "roles"."id" = "roles_users"."role_id" WHERE "roles_users"."user_id" = 1 AND "roles"."id" = 1 LIMIT 1
CACHE (0.0ms) SELECT "roles".* FROM "roles" WHERE (name = 'admin' and authorizable_type = 'System' and authorizable_id IS NULL) LIMIT 1
CACHE (0.0ms) SELECT 1 AS one FROM "roles" INNER JOIN "roles_users" ON "roles"."id" = "roles_users"."role_id" WHERE "roles_users"."user_id" = 1 AND "roles"."id" = 1 LIMIT 1
CACHE (0.0ms) SELECT "roles".* FROM "roles" WHERE (name = 'admin' and authorizable_type = 'System' and authorizable_id IS NULL) LIMIT 1
CACHE (0.0ms) SELECT 1 AS one FROM "roles" INNER JOIN "roles_users" ON "roles"."id" = "roles_users"."role_id" WHERE "roles_users"."user_id" = 1 AND "roles"."id" = 1 LIMIT 1
Rendered layouts/_admin_bar.html.haml (5.1ms)
Rendered shared/_facet.html.haml (0.8ms)
Rendered shared/_facet.html.haml (1.9ms)
Rendered shared/_facets.html.haml (4.8ms)
Rendered layouts/_main_body_no_h2.html.haml (5.5ms)
Rendered works/index.html.haml within layouts/application (18.2ms)
Completed 500 Internal Server Error in 31ms

ActionView::Template::Error (incompatible character encodings: UTF-8 and ASCII-8BIT):
8: .facet_heading #{heading}
9: %ol.facet_filters.top_facets
10: - facets.first(5).each do |f|
11: %li.show
12: = add_filter(params, filter_name, f.name, f.value)
13:
14: - if @facets[:publications].size > 5
app/views/shared/_facet.html.haml:11:in block in _app_views_shared__facet_html_haml__4311601692166166776_58314520'
app/views/shared/_facet.html.haml:10:ineach'
app/views/shared/_facet.html.haml:10:in _app_views_shared__facet_html_haml__4311601692166166776_58314520'
app/views/shared/_facets.html.haml:32:in_app_views_shared__facets_html_haml__857719063420239928_58169800'
app/views/works/index.html.haml:23:in block in _app_views_works_index_html_haml__2323343943641907598_55494600'
app/views/layouts/_main_body_no_h2.html.haml:3:in_app_views_layouts__main_body_no_h__html_haml__2008577892730596382_45081340'
app/views/works/index.html.haml:14:in `_app_views_works_index_html_haml__2323343943641907598_55494600'

I found some similar issues here: http://stackoverflow.com/questions/5286117/incompatible-character-encodings-ascii-8bit-and-utf-8 but they are related to mysql database. Ι even installed MySQL and tried to use greek characters but the same error appeared.
Can anyone propose a solution?