The galleries are here and here .

Permissions should be 755. However, I highly recommend Admin Tools from Akeeba Backup for fixing issue like this.

Thank you for your reply, Katia.

I tried setting the Folder permissions to 755 in my FTP client, but then the gallery does not appear.
I also installed Akeeba Admin Tools, which slows down my Joomla! CMS backend entirely. I had this experience earlier with Akeeba Back up.

Allow me to kindly point out that I only purchased SIG Pro, and did not sign up for installing additional plugins.

So, basically what I have is a bike without brakes and you don't sell any brakes.

If all the Joomla! extensions had the same server requirements as SIG Pro has, I'd plainly agree to your suggestion. However, in the documentation about SIG Pro it doesn't say anywhere that Admin Tools is pre-required to use SIG Pro.

It's a pity because it's a great tool with nice lay out and effects to look at.

Admin Tools -which is free by the way-is not prerequired.
In SIG PRO documentation it is clearly stated that your permissions should be set correct and Admin Tools can fix the permissions as the should be...
Fotis asked you to upgrade to the latest SIG PRO version too...

Thank you for your reply Katia.
I did upgrade to the latest version of SIG Pro. Thank you for pointing it out.

I also wrote a little story for Joomlaworks, a sort of allegory to illustrate my experience in solving this issue.

A lady wanted to cook something special

One day, a lady went to the market to buy some vegetables. She wanted to make a delicious soup for her husband and was needed the right ingredients. It took her a while to find them. She still thought there was something missing--something that would make the soup special. Then she passed by a market stand that she hadn't noticed before. Behind it was a polite looking farmer and on display, a vegetable she had never seen before. She asked the farmer what it could be used for.
“This will make an excellent soup”, the farmer replied, and the lady thought: “That is exactly what I need!”
“How do I use it?” she asked the farmer.
“With water and herbs”, the farmer replied. “It's not so difficult. Others have done it!”
The farmer's reply made her believe it was easy and self-explanatory, so she bought the vegetable and took it home.

Once at home, though, she couldn't figure out how to prepare the vegetable. She tried frying, boiling, steaming but it never turned out well. At last she went back to the market to ask for more instructions.
“Mr. Farmer,” she said, “I have cooked a lot of different vegetables in my life, but I can't figure out how to prepare this one. Can you give me some instructions?”
The farmer replied to her: “I am sorry to hear that. Look, I don't have a lot of time right now, but I should have told you that you need a special type of pan to prepare it in. There's a potter in the next village, who makes them, why don't you go visit him and buy one?

The lady thought it was a bit cumbersome but she had vowed to prepare something special and she was determined. She went to the next village, found the potter in a workshop and asked him if he could sell her a pan.
The potter looked at the lady and said: “I'm in a good mood today, so I'll get you one for free. How's that? If it doesn't work for you, you can always return it.” He offered her an odd-shaped pan that she had never seen before. “Don't forget the oil!” he added.
The lady's first thought was: “If it's free, can it be any good?” but she accepted the gift and bore in mind that she had already spent money on the vegetables, so why spend more than needed?

Back at home, she tried the pan as soon as she could heat up the stove. In went the water, the oil, the vegetable, herbs and spices and she was ready to go--or so she thought. Still, the vegetables wouldn't turn tender somehow, no matter what she tried to heat up the pan.
She went back to the farmer once more. From the look on his face she could tell he was getting a bit impatient with her, but she insisted on getting this special vegetable cooked in her soup.

After listening to her story, the farmer asked her: “Well, what sort of stove do you use?”
She explained to him that it was an ordinary stove that one could find in almost every household.
“I know the type you are talking about, but there are some levers that will open valves which you need to adjust for your stove to heat up properly. When you do that, it'll radiate a special heat which will make the vegetable turn tender. Didn't the potter tell you that?”
By now she was getting tired and fed up. “Actually, he didn't tell me that. But if using his pan to cook your vegetable forces me to run risks of being burned, I don't think it's worth it. It was already close to overheating when I tried it just before!”

The farmer only repeated himself: “Please go to the potter and ask him how to solve your problem.”