Try this: launch iPhoto with the Option key held down and create a new, test library. Import some photos and check to see if the same problem persists. If it doesn't then you current library is the culprit.
In that case make a temporary, backup copy of your library if you don't already have one (Control-click on the library and select Duplicate from the contextual menu) and apply the two fixes below in order as needed:
Launch iPhoto with the Command+Option keys held down and rebuild the library.
Since only one option can be run at a time start with Option #3, followed by #4 and then #1 as needed.
Using iPhoto Library Manager to Rebuild Your iPhoto Library
1 - download iPhoto Library Manager and launch.
2 - click on the Add Library button, navigate to your Home/Pictures folder and select your iPhoto Library folder.
3 - Now that the library is listed in the left hand pane of iPLM, click on your library and go to the File ➙ Rebuild Library menu option.
4 - In the next window name the new library and select the location you want it to be placed.
5 - Click on the Create button.
Note: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments. However, books, calendars, cards and slideshows will be lost. The original library will be left untouched for further attempts at fixing the problem or in case the rebuilt library is not satisfactory.
You might consider using Mail as your email client instead of iPhoto. Mail has photo stationary similar to iPhoto's themes and is easier to add multiple addresses and provides a Sent copy.
Thanks for the quick reply.
I tried Fix #1 and had the same problem which indicates it isn't a library problem. Photos insert okay and emails send fine but I just can't add text or captions. I normally use Yahoo mail but occasionally want to sent a photo via iPhoto and also have a book project in mind. This problem started in the last couple of months.
Thanks for your advice. I was reluctant to do a reinstall so I went on a search for other possible causes. I finally tracked it down to when I tried installing an old Bamboo pen tablet. In Systems I found an 'Ink' icon in which I had pen/handwriting gestures ticked. I unticked it and all is now working fine. Odd that the iPhoto sharing was the only place that the problem showed up. Thanks again.