Some solutions that might work , i know some was suggested just posting a list i made .
-Run you "Samp" as admin.
-Allow it throw your file wall.
-If you have any anti-vruis , turn it off quick then test it , and then you can see if it your ant-virus blocking it.
-Change your Screen resolution.
-Reinstall samp.
-Delete you're "gta_set" --> Its your "My documents" - "GTA San andeas User files".
-Right click on gta_sa.exe (in your GTA: San Andreas folder), then click on "Properties", then "Compatibiliy", then select "Run this program as administrator"
- Look for it maybe here : C:\Users\<YourComputerName>\AppData\Local\VirtualS tore\Program Files\Rockstar Games\GTA San Andreas
-Make sure you're screen shot folder is not full
-Where you screen shot save in My document must sure you set permissions to allow "right click it and choose "Properties". Then choose "Security" and make sure that all users have "Allowed" permissions for this folder.'
-If not try to restore you're GTA folder to a previous date when it was working
-Remove all you're screen shots from you're folder then re-install samp
-Update your Graphic drivers
If that does not work let us know