Even though this thread is a little old, I feel that I should point out what the actual issue is for the others who are getting such issue.
This is likely to do with mod_security2. You'll need to go to the control panel, security, mod_security, find the rule ID triggered in its log, and add it to the disabled rules file (there should be a hyperlink to it there).
This is what I currently use (and pMA is having no issues for me ever since):
## phpMyAdmin ##
SecRuleRemoveById 981205
SecRuleRemoveById 970901
SecRuleRemoveById 960915
SecRuleRemoveById 981001
SecRuleRemoveById 981318
SecRuleRemoveById 981317
SecRuleRemoveById 950001
SecRuleRemoveById 950006
SecRuleRemoveById 981244
SecRuleRemoveById 981249