"You need to migrate the form maker tables from Joomla 1.5 database to Joomla 2.5 database. To do that you need to:
Please uninstall the Form Maker if you have it installed then proceed with the following steps
1. go to phpMyAdmin
2. open your Joomla 1.5 database
3. select the Export menu item
4. change the radio button from Quick to Custom
5. unselect all tables and select the following 4 tables:
[j1_prefix]_formmaker
[j1_prefix]_formmaker_submits
[j1_prefix]_formmaker_themes
[j1_prefix]_formmaker_views
(where [j1_prefix] is your Joomla 1.5 database prefix)
6. scroll all the way down and press the Go button. This will export a SQL file containing those 4 tables.
7. go to your Joomla 2.5 database
8. select the Import menu item
9. browse for the exported SQL file
10. scroll all the way down and press the Go button. This will import the form maker tables to your Joomla 2.5 database.
-- now you need to change the prefix for those tables to the one that is set for your Joomla 2.5 database.
11. in the phpMyAdmin from the left pane of your Joomla 2.5 database select the [j1_prefix]_formmaker table.
12. select the Operations menu item from the top menu
13. scroll to the Table options box and edit the value of Rename table to field with the Joomla 2.5 prefix, so that the table name now looks like this [j2_prefix]_formmaker (where [j2_prefix] is your Joomla 2.5 database prefix)
14. do the same for other 3 tables.
15. go to your Joomla 2.5 administration panel and install the Form Maker 2.5 version.

That's it! Now you should have your forms, submissions and themes all set up. "

Hey, I've done everything as described but not installed.
This error code shows:

Warning
Duplicate entry '1' for key 'PRIMARY' SQL=INSERT INTO `#__formmaker` VALUES(1, 'A mailing list', '', '
%1 - custom_1%
%2 - Your Email Address:%
%3 - Word Verification:%
%4 - type_submit_reset_4%
', 7, '// Occurs before the form is loaded\r\nfunction before_load()\r\n{\r\n\r\n}\r\n\r\n// Occurs just before submitting the form\r\nfunction before_submit()\r\n{\r\n\r\n}\r\n\r\n// Occurs just before resetting the form\r\nfunction before_reset()\r\n{\r\n\r\n}', '', '', 1, '

%all%
', '

%all%
', 5, 1, '2#**id**#Your Email Address:#**label**#type_submitter_mail#****#3#**id**#Word Verification:#**label**#type_captcha#****#4#**id**#type_submit_reset_4#**label**#type_submit_reset#****#', '2#**id**#Your Email Address:#**label**#type_submitter_mail#****#3#**id**#Word Verification:#**label**#type_captcha#****#4#**id**#type_submit_reset_4#**label**#type_submit_reset#****#', 0, 'none', 'false', 'true', '', '', '', 0, 'testmode', '', 'USD', 0, '1*:*id*:*type_section_break*:*type*:*custom_1*:*w_field_label*:*
Join the mailing list (Sample)
*:*w_editor*:**:*new_field*:*2*:*id*:*type_submitter_mail*:*type*:*Your Email Address:*:*w_field_label*:*150*:*w_field_label_size*:*top*:*w_field_label_pos*:*200*:*w_size*:**:*w_first_val*:**:*w_title*:*yes*:*w_required*:**:*w_unique*:**:*w_class*:**:*new_field*:*3*:*id*:*type_captcha*:*type*:*Word Verification:*:*w_field_label*:*150*:*w_field_label_size*:*top*:*w_field_label_pos*:*6*:*w_digit*:**:*w_class*:**:*new_field*:*4*:*id*:*type_submit_reset*:*type*:*type_submit_reset_4*:*w_field_label*:*Submit*:*w_submit_title*:*Reset*:*w_reset_title*:**:*w_class*:*true*:*w_act*:**:*new_field*:*', 1, 1, '*', '', '', '', '', 1, '', '', '', '', '', '', '', '', '', '', '', 1, 1, 1, 1, '1,2,3,4,5,6,7,8,9,',1);
Package Install: There was an error installing an extension: com_formmaker.zip
Error
Error installing package

I managed to install it, the admins appear data but not the front page only shows a white page.

Something solution?

Thanks

Dear Papys,

Unfortunately your forms will not function properly if you transfer them from a Joomla 1.5 site to Joomla 3.5. The reason is that Joomla 1.5 Form Maker has not been developed further after Joomla stopped supporting Joomla 1.5.

So please uninstall the transferred Form Maker from your Joomla 3.5 site and install it fresh. Unfortunately you need to rebuild your forms of Joomla 1.5 site, but this would be the best choice anyway, because even if the forms of Joomla 1.5 site did transfer properly, they could not have the features latest Joomla 3.5 Form Maker provides.

Thank you!

I do not understand!

When 1.5 to 2.5 can migrate away why not 3.5 away as well?

If I migrate from 2.5, it can upgrade from 3.5?

Thanks

Dear Papys,

You can try to migrate to Joomla 2.5, then to 3.5, however, we cannot guarantee that the extension will work that way. So the best solution still would be to recreate your forms on Joomla 3.5 with latest version of Form Maker.

Thank you!

I understand the only problem is that very, very lot of form to do it again. the work would be huge

Dear Papys,

Did you try to migrate from 1.5 to 2.5 and then to 3.5? Please let me know if it worked properly and if there is anything else you'd like us to assist you with.

Thank you!

Unfortunately we did not succeed. Even the 2.5 migrate a similar error message appeared. Now do it again forms.

Dear Papys,

That's a pity that it did not work, but you will have the best results by rebuilding your forms. And in case you need help with recreating them, please don't hesitate to let me know.

I will get someone to help you recreate your forms.
Thank you!