11. STOCKHOLDERS' EQUITY AND STOCK-BASED COMPENSATION (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Total intrinsic values of options exercised	$ 152	$ 160	$ 338
Weighted average contractual life of the options exercisable and expected to be exercisable	3 years 6 months 7 days
Exercisable options to purchase (in thousands)	2,045	2,203	2,314
Weighted average exercise prices	$ 2.26	$ 2.25	$ 2.14
Restricted Stock Units granted (in thousands)	170	10	0
Shares withheld for taxes and not issued (in thousands)	9	6
Market value on the date of the grant	$ 1.92	$ 1.64
RSUs vested (in thousands)	37	13	16
RSUs unvested (in thousands)	132	10	23
Intrinsic value of RSUs, nonvested	$ 297	$ 16	$ 40
Stock Option and RSU
Stock-based compensation expense related to stock options and RSUs	$ 993	$ 751	$ 650
RSUs cancelled (in thousands)	1		8
2016 Equity Incentive Plan
Unrecognized stock-based compensation	$ 1,022
Estimated forfeitures of unvested stock based awards, amount	$ 3
Weighted average period for recognition of costs	2 years 4 months 24 days
Shares reserved for issuance (in thousands)	3,435
Authorized shares (in thousands)	4,036	4,813
Outstanding shares (in thousands)	2,898	3,163
Employee Stock Purchase Plan
Unrecognized stock-based compensation	$ 229
Weighted average period for recognition of costs	1 year 2 months 12 days
Stock-based compensation related to the ESPP	$ 108	$ 159	$ 255
Maximum calendar year contribution per employee	$ 25	$ 25	$ 25
Maximum number of shares a participant may purchase (in thousands)	3	3	3
ESPP purchase right granted (in thousands)	279	55	379
ESPP shares issued (in thousands)	147	136	125
Total shares issued under ESPP plan (in thousands)	1,764
ESPP Shares available for issuance (in thousands)	436
2006 Equity Incentive Plan
Shares remained available under plan (in thousands)	1,835
Board Of Directors
Restricted Stock Units granted (in thousands)	161	9	0
Market value on the date of the grant	$ 1.81	$ 1.64